Apparatus for controling servo signal gains of an optical disc drive and method of same

ABSTRACT

The invention provides an apparatus for controlling servo signal gains of an optical disc drive. The apparatus adjusts the gains of a plurality of servo signals controlling a servo system of the optical disc drive according to a closed-loop mode or a state-reloading mode whenever the optical disk drive encounters an operating state transition. In closed-loop mode, at least one AGC loop of the apparatus compensates the gains of the servo signals with a selectable bandwidth during a specific period after the operating state transition to accelerate the convergence of the servo signals. In state-reloading mode, at least one AGC loop of the apparatus reloads the previously saved convergence values or pre-determined values as the initial values according to the current operating state immediately after the operating state transition to accelerate the convergence of the servo signals.

CROSS REFERENCE TO RELATED APPILCATIONS

This application claims the benefit of U.S. Provisional Application No.60/803,874, filed Jun. 5, 2006, U.S. Provisional Application No.60/803,875, filed Jun. 5, 2006, U.S. Provisional Application No.60/803,887, filed Jun. 5, 2006, U.S. Provisional Application No.60/810,991, filed Jun. 5, 2006, U.S. Provisional Application No.60/810,972, filed Jun. 5, 2006, U.S. Provisional Application No.60/810,989, filed Jun. 5, 2006, U.S. Provisional Application No.60/811,031, filed Jun. 5, 2006, U.S. Provisional Application No.60/811,017, filed Jun. 5, 2006, U.S. Provisional Application No.60/810,990, filed Jun. 5, 2006, and U.S. Provisional Application No.60/810,898, filed Jun. 5, 2006. Each of these provisional applicationsis hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to optical disc drives, and more particularly tothe servo systems of optical disc drives.

2. Description of the Related Art

A servo system of an optical disc drive controls operations of thepickup head and the disc motor to read optical discs of differentformats in different conditions. A plurality of servo signals is used torespectively control different aspects of the servo system. For example,a tracking error signal controls tracking of the servo system, and afocusing error signal controls focus of the servo system. The servosignals are synthesized according to the reflection signals of amain-beam and a sub-beam, both laser beams projected onto the surface ofthe optical disc by the pickup head. To obtain reliable servo signals indifferent operating conditions of the optical disc drive, the servosignals require appropriate gain compensation in the synthesis thereof,and a mechanism for precisely controlling the servo signal gains is thusrequired.

FIG. 44 is a schematic diagram of the focused spots of a main-beam andtwo sub-beams incident on the surface of an optical disc. Data isrecorded on the grooves of the surface of the optical disc in the formof pits or spaces. When a focused spot of a laser beam is projected onthe groove, the reflection intensity of the laser beam is determinedaccording to whether a pit or a space is located at focused spot, anddata is thus read according to the reflection intensity. The focusedspot 7102 of the main-beam is projected on the groove N by the pickuphead and moves along the groove N to read data recorded thereon, and thefocused spots 7104 and 7106 of the two sub-beams are respectivelyprojected on the lands N and N−1 next to the groove N. The reflectionintensities of the main-beam and the sub-beams are then detected byphoto-detectors of the pickup head. The servo signals are synthesizedaccording to the reflection intensities, and the servo system is thencontrolled according to the servo signals to improve data reading.

However, when the reflectivity of a read portion of the optical discsurface is changed, the signal strengths detected by the photo-detectorsalso change, affecting the reliability of synthesized servo signals. Forexample, the reflectivity of the blank zone on which no data is recordedis different from the reflectivity of the data zone on which some datais recorded. If the read portion of the optical disc is switched fromthe blank zone to the data zone, the signal strength levels of the servosignals will vary due to the reflectivity difference. Thus,amplification adjustment of the servo signals is required toautomatically compensate the effect of the reflectivity difference, tomaintain servo signal strength at the same level in differentreflectivity conditions.

Additionally, if the intensity of a main-beam incident to the opticaldisc is changed, amplification adjustment of the servo signals may bealso required. FIG. 45 is a schematic diagram contrasting thereflectivity of the optical disc surface to the intensity of themain-beam. When the intensity of the main-beam is increased, thereflection intensity of the main-beam received by photo-detectorsdeclines because the surface of the groove melts due to the raisedintensity of the main-beam. When the groove surface melts, data iswritten to the surface of the groove. However, the reflection intensityof the sub-beam remains at the same level. Because some of the servosignals are synthesized according to both reflection intensities of themain-beam and the sub-beam, the amplification adjustment of the servosignals is also required to balance the difference between thereflection intensities of the main-beam and the sub-beam, to maintainthe servo signal strength at the same level.

BRIEF SUMMARY OF THE INVENTION

An apparatus for controlling servo signal gains of an optical disc driveis provided. The apparatus adjusts the gains of a plurality of servosignals controlling a servo system of the optical disc drive accordingto a closed-loop mode or a state-reloading mode whenever the opticaldisk drive encounters an operating state transition, in which thereflectivity of an optical disc is changed. In closed-loop mode, atleast one AGC loop determining the gains of the servo signals iscompensated with a selectable bandwidth during a specific period afterthe operating state transition to accelerate the convergence of theservo signals. Or in state reloading mode, previously saved convergencevalues or pre-determined values determining the most possible gains ofthe servo signals are immediately reloaded to be the initial values ofat least one AGC loop after the operating state transition to acceleratethe convergence of the servo signals. After reloading of this previouslysaved convergence values or pre-determined values as the initial valuesof AGC loops, the requirement for the bandwidth of AGC loops can be notso high.

Another apparatus for controlling servo signal gains of an optical discdrive is provided. The apparatus includes a first automatic gain controlmodule and a second automatic gain control module. The first automaticgain control module adjusts a loop ratio of a main-beam to control thegains of a plurality of servo signals whenever the optical disk driveencounters changes in the reflectivity of an optical disc, wherein theservo signals control a servo system of the optical disc drive. Thesecond automatic gain control module adjusts the gains of the sub-beamservo signals according to a main-beam sub-beam ratio whenever theoptical disk drive encounters changes in the reflectivity of an opticaldisc, wherein the main-beam sub-beam ratio is calculated according toboth the reflection intensities of the main-beam and a sub-beamreflected from an optical disc.

A method for controlling servo signal gains of an optical disc drive isalso provided. A plurality of servo signals controls a servo system ofthe optical disc drive. The gains of the servo signals are adjustedaccording to a closed-loop mode or a state-reloading mode whenever theoptical disk drive encounters an operating state transition, in whichthe reflectivity of an optical disc is changed. In closed-loop mode, atleast one AGC loop determining the gains of the servo signals is thencompensated with a selectable bandwidth during a specific period afterthe operating state transition to accelerate the convergence of theservo signals. Or in state-reloading mode, previously saved convergencevalues or pre-determined values determining the most possible gains ofthe servo signals are immediately reloaded to be the initial values ofat least one AGC loop after the operating state transition to acceleratethe convergence of the servo signals.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 is a diagram illustrating the signal processing apparatusaccording to an embodiment of the present invention.

FIG. 2 is a diagram illustrating the analog adjusting modules of thepresent invention.

FIG. 3 is a diagram illustrating the digital adjusting modules of thepresent invention.

FIG. 4 is a block diagram of a servo signal generation module of FIG. 3;

FIG. 5A is a block diagram of a first AGC module according to theinvention;

FIG. 5B is a block diagram of a second AGC module according to theinvention;

FIG. 6 is a schematic diagram showing transient variation of a loopratio;

FIG. 7 is a block diagram of a gain control logic of the first ADCmodule of FIG. 5A;

FIG. 8 is a block diagram of a gain control logic of the second ADCmodule of FIG. 5B;

FIG. 9 shows an amplification process relating to generation of atracking error signal;

FIG. 10 shows an amplification process relating to generation of asub-beam addition signal;

FIG. 11 shows the timing of saving and reloading operations of first andsecond AGC modules in a state reloading mode; and

FIG. 12 shows converging processes of a loop ratio in high bandwidth andthe state reloading modes.

FIG. 13 is a block diagram illustrating a control system according to aembodiment of the present invention.

FIG. 14 is a diagram illustrating an automatic power control system ofan optical disc drive employing the architecture shown in FIG. 1.

FIG. 15 a block diagram illustrating an alternative DAC architectureaccording to an embodiment of the present invention.

FIG. 16 is a timing diagram illustrating the filter bandwidth adjustmentcontrolled by a filter controller shown in FIG. 3.

FIG. 17 is a block diagram illustrating a control system according to aembodiment of the present invention.

FIG. 18 is a diagram illustrating an automatic power control system ofan optical disc drive employing the architecture shown in FIG. 5.

FIG. 19 is a diagram illustrating another automatic power control systemof an optical disc drive employing the architecture shown in FIG. 5.

FIG. 20 is a schematic diagram of an APC system coupled to an OPUaccording to an embodiment of the present invention.

FIG. 21 is a diagram showing a straight line SL and a characteristiccurve CV of the LD shown in FIG. 5.

FIG. 22 is a schematic diagram of an APC system coupled to an OPUaccording to another embodiment of the present invention.

FIG. 23A is a flowchart of a first method of generating a zero crossingsignal of an optical disc drive according to an exemplary embodiment ofthe invention.

FIG. 23B is a flowchart of a second method of generating a zero crossingsignal of an optical disc drive according to another exemplaryembodiment of the invention.

FIG. 24 shows a signal processing apparatus for an optical disc driveaccording to an embodiment of the invention.

FIG. 25 shows generation of the TEZC signal based on the first method ofthe exemplary embodiment.

FIG. 26 shows generation of the TEZC signal based on the second methodof another exemplary embodiment.

FIG. 27 shows a signal processing apparatus for an optical disc driveaccording to another exemplary embodiment of the invention.

FIG. 28 shows a signal processing apparatus for an optical disc driveaccording to another exemplary embodiment of the invention.

FIG. 29 shows a signal processing apparatus of an optical disc driveaccording to an exemplary embodiment of the invention.

FIG. 30 shows a signal processing apparatus of an optical storage deviceaccording to another exemplary embodiment of the invention.

FIG. 31 shows a signal processing apparatus of an optical storage deviceaccording to further another exemplary embodiment of the invention.

FIG. 32 is a flowchart showing operation of the control module inconjunction with the selector in FIG. 31.

FIG. 33 shows a signal processing apparatus of an optical storage systemaccording to yet another embodiment of the invention

FIG. 34 is a block diagram illustrating an exemplary embodiment of anapparatus capable of determining a reference level according to an inputsignal and a reference signal and then processing the input signal usingthe determined reference level.

FIG. 35 is a timing diagram illustrating the generation of the referencelevel and the sliced signal shown in FIG. 34 according to an embodimentof the present invention.

FIG. 36 is a diagram illustrating the protection scheme according to anembodiment of the present invention.

FIG. 37 is a flow chart of processing an RFRP signal to generate amirror signal according to an embodiment of the present invention.

FIG. 38 is a diagram illustrating the structure of the digital signalprocessor of the signal processing apparatus according to an embodimentof the present invention.

FIG. 39 is a block diagram of an exemplary automatic power controlsystem according to the invention.

FIG. 40 is a block diagram of an exemplary down sampling circuitaccording to the invention, incorporated in the automatic controlcircuit in FIG. 39.

FIG. 41 is a timing diagram of selected signals according to theinvention, incorporated in the down sampling circuit in FIG. 40.

FIG. 42 is a flowchart of an exemplary automatic control circuit method,incorporated in the automatic control circuit in FIG. 39.

FIG. 43 is a flowchart of an exemplary down sampling method,incorporated in the method in FIG. 42 and the down sampling circuit inFIG. 40.

FIG. 44 is a schematic diagram of the focused spots of a main-beam andtwo sub-beams incident on the surface of an optical disc.

FIG. 45 is a schematic diagram contrasting the reflectivity of theoptical disc surface with the intensity of the main-beam.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

Please refer to FIG. 1. FIG. 1 is a diagram illustrating the signalprocessing apparatus 200 according to an embodiment of the presentinvention. The signal processing apparatus 200 comprises 8 sample andhold units 201˜208, 8 analog adjusting modules 211˜218, a multiplexer240, an Analog to Digital Converter (ADC) 250, a de-multiplexer 260, 8digital adjusting modules 261˜268, a digital servo error signalgenerator 280, and a signal holding controller 295.

The sample and hold units 201˜208 respectively receive photo diodesignals A, B . . . H from photo diodes (or called PDIC) of the opticalpickup, and hold the received photo diode signals according to thecontrol signal S4. For example, when the signal holding controller 295transmits the control signal S4, the sample and hold unit 201 outputsthe current photo diode signal A. On the other hand, when the signalholding controller 295 does not transmit the control signal S4, thesample and hold unit 201 outputs the previous sampled photo diode signalA instead of the current photo diode signal A.

The signal holding controller 295 is coupled to the sample and holdunits 201˜208 for generating the control signal S4. Thus, the holdingactions of the sample and hold units 201˜208 are all controlled by thesignal holding controller 295. For example, the signal holdingcontroller 295 can transmit the control signal S4 when the optical discdrive operates in the read state, or transmit the control signal S4 inthe period that the analog photo diode signals A˜H are in the constantmanner similar to the read power when the optical disc drive operates inwrite state. Moreover, the signal holding controller 295 can alwaystransmit the control signal S4 so that the sample and hold units alwayssample analog photo diode signals.

Each of the analog adjusting modules 211˜218 comprises an amplifier, ananalog offset unit, and an Anti-Alias Filter (AAF). For example, thefirst adjusting module 211 comprises an amplifier 311, an analog offsetunit 221, and an AAF 231. Each of the digital adjusting modules 261˜268comprises a digital offset unit. For example, the digital adjustingmodule 261 comprises a digital offset unit 271.

The analog adjusting modules 211˜218 are respectively coupled to thesample and hold units 201˜208 for receiving the sampled photo diodesignals A-H output from the sample and hold units 201˜208 and amplifyingthe received photo diode signals. The gains of the analog adjustingmodules 211˜218 are appropriately controlled for increasing signalqualities of the amplified analog photo diode signals.

The analog offset units 221˜228 are respectively coupled to the analogadjusting modules 211˜218 for receiving the amplified photo diodesignals A˜H output from the analog adjusting modules 211˜218 andoffsetting the amplified photo diode signals A˜H. The offset values ofthe analog offset units 221-228 are appropriately controlled so that theanalog photo diode signals after being offset can fall within the inputsignal ranges of the multiplexer 240 and the ADC 250.

The AAFs 231˜238 are respectively coupled to the analog offset units221˜228 for receiving the offset photo diode signals A˜H output from theanalog offset units 221˜228 and filtering the offset photo diode signalsA˜H.

The multiplexer 240 comprises 8 input ends and an output end. Each ofthe input ends of the multiplexer 240 is respectively coupled to thecorresponding AAF for receiving the filtered photo diode signal. Themultiplexer 240 couples the 8 input ends of the multiplexer 240selectively to the output end of the multiplexer 240. The sequence ofthe input ends of the multiplexer 240 coupled to the output end of themultiplexer can be in sequential or programmable. In this way, theoutput end of the multiplexer 240 outputs the filtered photo diodesignals A˜H at different time.

The ADC 250 is coupled to the output end of the multiplexer 240 forreceiving signals from the multiplexer 240 and accordingly convertingthe received signals into digital signals. In this way, the filteredanalog photo diode signals A˜H are converted into digital photo diodesignals A″˜H″ in different periods.

The de-multiplexer 260 comprises 8 output ends and an input end. Theinput end of the de-multiplexer 260 is coupled to the ADC 250 forsequentially receiving the digital photo diode signals A″˜H″. Thede-multiplexer 260 couples the 8 output ends of the de-multiplexer 260sequentially to the input end of the de-multiplexer 260. In this way,the output ends of the de-multiplexer 260 respectively output thedigital photo diode signals A″˜H″.

The digital offset units 271˜278 are respectively coupled to the outputends of the de-multiplexer 260 for respectively receiving the digitalphoto diode signals A″˜H″. For example, the digital offset unit 271receives the digital photo diode signal A″, the digital offset unit 272receives the digital photo diode signal B″, and so on. The digitaloffset units 271˜278 offset the received digital photo diode signalsA″˜H″. The offset values of the digital offset units 271˜278 areappropriately controlled so as to offset the received digital photodiode signals A″˜H″. Thus, the level of each digital photo diode signalsA″˜H″ could be set to a pre-determined value after digital offset.

The spirit of the present invention disposing digital offset units is toreduce the offsets of the photo diode signals caused by the componentsthe photo diode signals pass through. If the photo diode signals areonly adjusted once by the analog offset units 221˜228, the offset ofphoto diode signals are still large even. Therefore, the digital offsetunits 271˜278 are disposed for completely centering the photo diodesignals.

The digital servo signal generator 280 is coupled to the digital offsetunits 271˜278 for receiving the offset digital photo diode signalsA″˜H″. The servo signal generator 280 generates digital servo signals bycomputation on the received digital photo diode signals A″˜H″. Thedigital servo signals can be a focusing error signal FE or a trackingerror signal TE, for example. The focusing error signal FE is generatedaccording to the equation: FE=(A″+C″)−(B″+D″). The Push-Pull trackingerror signal TE is generated according to the equation:TE=[(A″+D″)−(B″+C″)]−α*[(E″+H″)−(F″+G″)].

After the digital servo signal generator 280 generates the digital servosignals, the digital servo signals are transmitted to the servocontroller 290. Thus, the servo controller 290 can execute servocontrols according to the received digital servo signals. The servocontrol can be focusing control, tracking control, and seeking control.

The signal processing apparatus 200 of the present invention providessample and hold units for a user to choose particular periods of theanalog photo diode signals for signal processing. That is, the user canselect particular periods of the analog photo diode signals for signalprocessing and further generation of the digital servo signals whileother periods of the analog photo diode signals not selected areignored. Furthermore, the user can select periods of the analog photodiode signals having the same constant manner for signal processing. Inthis way, the components of the first adjusting modules and the secondadjusting modules can be designed with smaller input range, which reducethe product expenses and the design complexity.

The signal processing apparatus 200 of the present invention furtherprovides the multiplexer and the de-multiplexer for saving the amount ofADCs. In the present invention, only one ADC is needed for convertingall the analog photo diode signals.

Please refer to FIG. 2. FIG. 2 is a diagram illustrating the analogadjusting modules 211˜218 of the present invention. The gain of theamplifier of the analog adjusting module of the present invention can becontrolled according to the operation of the optical disc drive such asa write state or a read state. For example, in the analog adjustingmodule 211, the gain of the amplifier 311 is set to be a firstpredetermined value RGA when the optical disc drive operates in the readstate, and is set to be a second predetermined value WGA when theoptical disc drive operates in the write state. Each of the amplifiers311˜318 has its own predetermined values according to the states of theoptical disc drive. The signal S5 indicates the state of the opticaldisc drive. For example, the signal S5 may be a 1, meaning the opticaldisc drive operates in the write state. Consequently, the gain of eachamplifier is changed to the predetermined value of the write state. Onthe other hand, the signal S5 may be a 0, meaning the optical disc driveoperates in the read state. Consequently, the gain of each amplifier ischanged to the predetermined value of the read state.

Please continue referring to FIG. 2. The offset value of the analogoffset unit of analog adjusting module of the present invention can becontrolled according to the operation of the optical disc drive such aswrite state or read state. For example, in the analog adjusting module211, the offset value of the analog offset unit 221 is set to be a thirdpredetermined value ROA when the optical disc drive operates in the readstate, and set to be a fourth predetermined value WOA when the opticaldisc drive operates in the write state. Each of the analog offset units221˜228 has its own predetermined values according to the states of theoptical disc drive. The signal S5 indicates the state of the opticaldisc drive. For example, the signal S5 may be a 1, meaning the opticaldisc drive operates in the write state. Consequently, the offset valueof each analog offset unit is changed to the predetermined value of thewrite state. On the other hand, the signal S5 may be a 0, meaning theoptical disc drive operates in the read state. Consequently, the offsetvalue of each analog offset unit is changed to the predetermined valueof the read state.

Please refer to FIG. 3. FIG. 3 is a diagram illustrating the digitaladjusting modules 261˜268 of the present invention. The offset value ofthe digital offset unit of the digital adjusting module of the presentinvention can be controlled according to the operation of the opticaldisc drive such as write state or read state. For example, in thedigital adjusting module 261, the offset value of the digital offsetunit 271 is set to be a fifth predetermined value ROA2 when the opticaldisc drive operates in the read state, and set to be a sixthpredetermined value WOA2 when the optical disc drive operates in thewrite state. Each of the digital offset units 271˜278 has its ownpredetermined values according to the states of the optical disc drive.The signal S5 indicates the state of the optical disc drive. Forexample, when the signal S5 is 1, the optical disc drive operates in thewrite state. Consequently, the offset value of each digital offset unitis changed to the predetermined value of the write state. On the otherhand, when the signal S5 is 0, the optical disc drive operates in theread state. Consequently, the offset value of each digital offset unitis changed to the predetermined value of the read state.

FIG. 4 is a block diagram of a digital servo signal generator 400, anembodiment of the digital servo signal generator 280 of FIG. 1. Thedigital photo diode signals A″, B″, C″, and D″ of the main-beam arefirst delivered to a main-beam summation module 402, a main-beampush-pull module 404, and a main-beam focusing error module 406. Themain-beam summation module 402 generates a main-beam summation signal MSwhich indicates the summation of signals A″, B″, C″, and D″. Themain-beam push-pull module 404 generates a main-beam push-pull signal MPwhich indicates [(A″+D″)−(B″+C″)]. The main-beam focusing error module406 derives a main-beam focusing error signal MF according to signalsA″, B″, C″, and D″.

Accordingly, the digital photo diode signals E″, F″, G″, and H″ of thesub-beams are delivered to a sub-beam summation module 412, a sub-beampush-pull module 414, and a sub-beam focusing error module 416. Thesub-beam summation module 412 generates a sub-beam summation signal SSindicating the summation of signals E″, F″, G″, and H″. The sub-beampush-pull module 414 generates a sub-beam push-pull signal SP indicating[(E″+H″)−(F″+G″)]. The sub-beam focusing error module 416 derives asub-beam focusing error signal SF according to signals E″, F″, G″, andH″.

A tracking error (TE) signal generation module 424 then derives atracking error signal TE according to the main-beam push-pull signal MPand the sub-beam push-pull signal SP. A focusing error (FE) signalgeneration module 426 derives a focusing error signal FE according tothe main-beam focusing error signal MF and the sub-beam focusing errorsignal SF. A sub-beam addition (SBAD) signal generation module 422derives a current main-beam summation signal C_MS indicating the sum ofsignals A″, B″, C″, and D″ and a current sub-beam summation signal C_SSindicating the sum of signals E″, F″, G″, and H″ according to themain-beam summation signal MS and the sub-beam summation signal SS. TheSBAD signal may be the current main-beam summation signal C_MS or thecurrent sub-beam summation signal C_SS. Although only three servosignals TE, FE and SBAD are shown in FIG. 4, the servo signal generationmodule 400 may include modules generating other servo signals such as CEand RFRP signals in the ways similar to the generation of signals TE, FEor SBAD.

Although the servo signals TE, FE and SBAD are already generated, theservo signals require appropriate amplification to maintain the strengthof the servo signals at the same level in different operating conditionsof the optical disc drive. As noted, the gain levels of the servosignals require quick adjustment to make the servo system stablewhenever the optical disc drive encounters an operating state transitionin which the reflection of the optical disc varies much. For example,the operating state transition occurs when the read portion of theoptical disc is changed between a data zone and a blank zone, and whenthe operation of the optical disc drive is changed between write stateand read state.

Thus, an apparatus 430 for automatically adjusting the gains of theservo signals whenever the operating state transition occurs isprovided. The apparatus 430 includes a first automatic gain control(AGC) module 432 generating gain signals G₁₁, G₁₂, and G₁₃ according toa target level T_MS and the current main-beam sum signal C_MS. The SBADsignal generation module 422, the TE signal generation module 424, andthe FE signal generation module 426 then amplify the SBAD signal (theC_MS or T_MS signal), the TE signal, and the FE signal respectivelyaccording to the gain signals G₁₁, G₁₂, and G₁₃, to maintain the servosignal level at an identical level in different operating conditions.

The apparatus 430 also includes a second automatic gain control (AGC)module 434 generating gain signals G₂₁, G₂₂, and G₂₃ according to thecurrent main-beam sum signal C_MS and the current sub-beam sum signalC_SS. The sub-beam summation module 412, the TE sub-beam push-pullmodule 414, and the sub-beam focusing error module 416 then amplify theSS signal, the SP signal, and the SF signal respectively according tothe gain signals G₂₁, G₂₂, and G₂₃, to balance the difference betweenthe reflection intensities of the main-beam and the sub-beam.

FIG. 5A is a block diagram of the first AGC module 500 according to theinvention. The first AGC module 500 includes a loop ratio generationmodule 510, a gain control logic 530, and a data storage module 520. Thefirst AGC module 500 adjusts a loop ratio of the main-beam to controlthe gains G₁₁, G₁₂, and G₁₃ of the servo signals SBAD, TE, and FE duringoperating state. The loop ratio generation module 510 determines theloop ratio based on the target level T_MS and the current main-beamsummation signal C_MS . Because the loop ratio indicates the ratio ofthe desired level to the current level of the reflection intensity ofthe main-beam, the gains of the servo signals TE, FE, and SBAD can bedetermined according to the loop ratio, thereby compensating the servosignals to the desired level. The gain control logic 530 then determinesthe gain signals G₁₁, G₁₂, and G₁₃ according to the loop ratio signal.

After the gains G₁₁, G₁₂, and G₁₃ of the servo signals are determined,the servo signals FE,TE or SBAD could be adjusted accordingly. Theconvergence of G₁₁, G₁₂, and G₁₃, however, is quite slow, requiring along time for the servo signals to achieve the desired level underordinary amplification. FIG. 6 shows a schematic diagram showing thetransient variation of the loop ratio. The curve 610 indicates the loopratio variation under the ordinary amplification. An operating statetransition occurs at time t₁, but the loop ratio achieves the desiredlevel of V₁ at time t₅, delaying the amplification of the servo signals.

To accelerate the amplification convergence of the servo signals, twoAGC modes, a closed-loop mode and a state-reloading mode, are applied tothe operation of both AGCs of the servo signals when the optical discdrive encounters an operating state transition. If the first AGC module500 adopts the closed-loop mode only to amplify the servo signals, thegains of the servo signals could be compensated with a high bandwidthduring a specific period after the operating state transition, as shownby the curve 606 indicating the loop ratio variation under closed-cloopmode. It can be seen that the convergence time under high bandwidth modeis reduced to time t₃, and the convergence process is accelerated. Afterthis specific period, the bandwidth of AGCs could be switched to aslower one.

Another AGC mode is the state-reloading mode. The data storage module520 of the first AGC module 500 respectively saves convergence values ofthe loop ratios under different operating conditions in advance whilethe servo signals converges. If the first AGC module 500 adopts thestate-reloading mode to amplify the servo signals, the loop ratiogeneration module 510 immediately reloads the saved convergence value ofthe loop ratio or a pre-determined value corresponding to the currentoperating condition during operating state transition, and then assignsthis value to be the initial value of the loop ratio. Curve 602indicates the loop ratio variation under state reloading mode if theinitial value V₃ is close to the convergence value V₁, and theconvergence time is reduced to time t₂ to accelerate the convergenceprocess. Curve 604 indicates the loop ratio variation under statereloading mode if the initial value V₂ is far from the convergence valueV₁, and the convergence time is enlarged to time t₄. In state-reloadingmode, after the saved convergence value or a pre-determined value loadedas the initial value of AGC, AGC is switched to closed-loop again toadjust the loop ratio dynamically.

FIG. 5B is a block diagram of a second AGC module 550 according to theinvention. The second AGC module 550 includes a main-beam sub-beam ratiogeneration module 560, a gain control logic 580, and a data storagemodule 570. The second AGC module 550 adjusts the gains G₂₁, G₂₂, andG₂₃ of the sub-beam signals SS, SP, and SF according to a main-beamsub-beam ratio during operating state transition. The main-beam sub-beamratio generation module 560 determines the main-beam sub-beam ratio(MS_ratio) from the current main-beam summation signal C_MS and thecurrent sub-beam summation signal C_SS. Because the MS_ratio indicatesthe difference of the current levels of the reflection intensity of themain-beam and the sub-beam, the difference between the reflectionintensity of the main-beam and the sub-beam can be appropriatelybalanced according to the MS_ratio, thereby securing the accuracy of thesynthesis of the servo signals TE, FE, and SBAD. The gain control logic580 then determines the gain signals G₂₁, G₂₂, and G₂₃ according to theMS_ratio signal. Details of the gain control logic 580 are shown in FIG.8. Accordingly, the second AGC module 550 also adopts the closed-loopmode or the state-reloading mode in the amplification process of thesub-beam signals SS, SP, and SF to accelerate the signal convergenceduring operating state transition.

FIG. 7 is a block diagram of a gain control logic 700 of the first AGCmodule of FIG. 5A. A TE gain register 702, a FE gain register 704, and aSBAD gain register 706 respectively hold the gains of the servo signalsTE, FE, and SBAD. Three multipliers 712, 714, and 716 respectivelymultiply the gains of the servo signals TE, FE, and SBAD with the loopratio. A control module 710 determines three switch signals SW_TE,SW_FE, and SW_SBAD according to a write signal and a blank signal. Thewrite signal indicates the switch between the writing operation and thereading operation of the optical disc drive, and the blank signalindicates the switch between the blank zone and the data zone read bythe optical disc drive. Thus, the control module 710 can determine theoccurrence of the operating state transition according to both the writesignal and the blank signal to switch the gain level of the servosignals. The switch signals SW_TE, SW_FE, and SW_SBAD then select theoriginal gains or the multiplied gains as the actual gains G₁₂, G₁₃, G₁₁of the servo signals TE, FE, and SBAD.

FIG. 8 is a block diagram of a gain control logic 800 of the second AGCmodule of FIG. 5B. A SS gain register 802, a SP gain register 804, and aSF gain register 806 respectively hold the gains of the sub-beam signalsSS, SP, and SF. Three multipliers 812, 814, and 816 respectivelymultiply the gains of the sub-beam signals SS, SP, and SF with theMS_ratio. A control module 810 determines three switch signals SW_SS,SW_SP, and SW_SF according to the write signal and the blank signal.Accordingly, the control module 810 can determine the occurrence of theoperating state transition according to both the write signal and theblank signal to switch the gain level of the sub-beam signals. Theswitch signals SW_SS, SW_SP, and SW_SF then select the original gains orthe multiplied gains as the actual gains G₂₁, G₂₂, G₂₃ of the sub-beamsignals SS, SP, and SF.

FIG. 9 shows an amplification process relating to the generation oftracking error signal TE. The main-beam push-pull module 404 generatesthe main-beam push-pull signal MP according to the main-beam signals A″,B″, C″, and D″. The sub-beam push-pull module 414 generates the sub-beampush-pull signal SP according to the sub-beam signals E″, F″, G″, andH″. The second AGC module 434 generates a gain signal G₂₂ of thesub-beam push-pull signal SP to balance the signal strength differencebetween the main-beam and the sub-beam, and the sub-beam push-pullmodule 414 amplifies the sub-beam push-pull signal SP according to thegain signal G₂₂. A subtracter 902 of the TE signal generation module 424then subtracts the amplified SP signal from the MP signal to obtain thetracking error signal. The first AGC module 432 then determines a gainsignal G₁₂ of the tracking error signal to maintain the signal strengthat a constant level in different operating conditions, and theamplification module 904 then amplifies the tracking error signalaccording to the gain signal G₁₂. After filtration of the filtrationmodule 906, the tracking signal TE is output to the servo control module312 to control the tracking operation of the optical disc drive.

FIG. 10 shows an amplification process relating to generation of asub-beam addition signal SBAD. The main-beam summation module 402generates the main-beam summation signal MS according to the main-beamsignals A″, B″, C″, and D″. The sub-beam summation module 412 generatesthe sub-beam summation signal SS according to the sub-beam signals E″,F″, G″, and H″. The second AGC module 434 generates a gain signal G₂₁ ofthe sub-beam summation signal SS to balance the signal strengthdifference between the main-beam and the sub-beam, and the sub-beamsummation module 412 then amplifies the sub-beam summation signal SSaccording to the gain signal G₂₁. A multiplexer 1002 of the SBAD signalgeneration module 422 then selects the amplified SS signal or the MSsignal as the SBAD signal, which may be the current main-beam sum signalC_MS or the current sub-beam sum signal C_SS. The first AGC module 432then determines a gain signal G₁₁ of the SBAD signal to maintain thesignal strength at a constant level in different operating conditions,and the amplification module 1004 then amplifies the SBAD signalaccording to the gain signal G₁₁. After filtration of the filtrationmodule 1006, the SBAD signal is output to the servo control module 312.

FIG. 11 shows the timing of the saving and reloading operations of thefirst and second AGC modules in state reloading mode. As previouslyexplained, the write signal and the blank signal can determine theoccurrence of the operating state transition. For example, the readingportion of the optical disc is switched from a data zone to a blank zoneat time T1, and switched from a blank zone to a data zone at time T2.The operation of the optical disc drive is switched from reading towriting at time T3, and switched from writing back to a reading at timeT4. Each of the times T1˜T5 corresponds to an operating statetransition, and the saving and reloading operations are also executed ateach operating state transition.

For example, because the read portion of the optical disc drive isswitched from a data zone to a blank zone at time T1, the loop ratiogeneration module 510 of the first AGC module 500 immediately saves thecurrent converged value of the loop ratio corresponding to the previousdata state into the data storage module 520 in state reloading mode. Atthe same time, the loop ratio generation module 510 retrieves thepreviously saved loop ratio value corresponding to the current blankstate from the data storage module 520 and directly assigns thepreviously saved loop ratio value to be the initial value of the loopratio. Moreover, because the operation of the optical disc drive isswitched from reading to writing at time T3, the main-beam sub-beamratio generation module 560 of the second AGC module 550 immediatelysaves the current converged value of the MS_ratio corresponding to theprevious data state into the data storage module 570 in state reloadingmode. At the same time, the main-beam sub-beam ratio generation module560 retrieves the previously saved MS_ratio value corresponding to thecurrent write state from the data storage module 570 and directlyassigns the previously saved MS_ratio value to be the initial value ofthe MS_ratio.

FIG. 12 shows converging processes of the AGC loop in closd-loop modeand state-reload mode. Each of the times T1˜T5 corresponds to anoperating state transition as in FIG. 11. The loop ratio 1 shows theconverging process of the AGC loop ratio in closed-loop mode only, andthe loop ratio 2 shows the converging process of the AGC loop ratio inthe combination of state-reload and closed-loop mode. The Bandwidth ofAGC loop is selectable. Because the loop ratio 1 could be acceleratedwith a high bandwidth during a specific period after the operating statetransition, rapid convergence of the loop ratio 1 could be attained.Additionally, because previously saved convergence values of the loopratio or any pre-determined values are immediately assigned to be as theinitial values of the loop ratio 2, the loop ratio 2 immediatelyconverges to the correct level to accelerate the convergence of theservo signals.

The invention provides an apparatus for controlling servo signal gainsof an optical disc drive. Generation of the servo signal anddetermination of gain adjustment thereof are implemented in digitaldomain, thereby facilitating the gain adjustment of the servo signals.The apparatus includes a first AGC module adjusting the loop ratio todetermine the gain adjustment, thereby maintaining the strength of theservo signals at a constant under different operating conditions. Theapparatus also includes a second AGC module adjusting a main-beamsub-beam ratio to determine the gain adjustment, thereby balancing theintensity difference of the main-beam and the sub-beam in differentoperating conditions. Additionally, the apparatus adopts a combinationof closed-loop mode and state-reload mode to accelerate the convergenceof the servo signals during the gain adjustment.

Besides the signal processing apparatus for generating the digital servosignals, another digital part of the optical disc drive is digital autopower control system. Please refer to FIG. 13. FIG. 13 is a blockdiagram illustrating a control system 1100 according to an embodiment ofthe present invention. As shown in FIG. 13, the control system 1100comprises a target circuit 1102 (e.g. an optical pick-up unit (OPU)), astate decision circuit 1104, a plurality of buffers 1106-1, 1106-2,1106-3, . . . , 1106-N, a multiplexer (MUX) 1108, a controlling circuit1112, and a switch 1114. The state decision circuit 1104 is implementedfor generating a state decision signal Sd according to a selectedoperational state of the target circuit 1102; the buffers 1106-1,1106-2, 1106-3, . . . , 1106-N are implemented for storing a pluralityof control data corresponding to a plurality of candidate operationalstates of the target circuit 1102 respectively. The multiplexer 1108 iscoupled between the state decision circuit 1104 and buffers 1106, and isimplemented for coupling a selected buffer from the buffers 1106-1,1106-2, 1106-3, . . . , 1106-N to a digital-to-analog converter (DAC)1110 according to the state decision signal Sd for outputting a controldatum stored in the selected buffer to the DAC 1110. In this embodiment,the target circuit 1102 (e.g. a laser diode in an optical pick-upunit(OPU)) is a circuit configured to receive an analog input forfurther processing, and the DAC 1110 is coupled between the multiplexer1108 and the target circuit 1102 for converting the control datum (i.e.digital datum) into an analog control signal (e.g. a control voltage ora control current) and outputting the analog control signal to thetarget circuit 1102. It should be noted that in other embodiments wherethe target circuit 1102 is a circuit configured to receive a digitalinput for further processing, the DAC 1110 can be omitted. In otherwords, the DAC 110 is an optional component, depending upon designrequirements.

The controlling circuit 1112 is coupled to the target circuit 1102, andis implemented for determining the control datum of the selectedoperational state according to an operation of the target circuit 1102.As shown in FIG. 13, the controlling circuit 1112 includes a sensor1116, an analog-to-digital controller (ADC) 1118, and a digitalcontroller 1120. In this embodiment, the target circuit 1102 (e.g. alaser diode in an optical pick-up unit) is a circuit configured tooutput a non-electrical signalt, and the sensor 1116 (e.g. a photodetector) is implemented to convert the non-electrical signal into acorresponding analog electrical signal. The ADC 1118 converts theincoming analog electrical signal into a digital value and outputs thedigital value to the digital controller 120. Next, the digitalcontroller 1120 determines and updates the control datum of the selectedoperational state of the target circuit 1102. Please note that thesensor 1116 is not limited to detect the non-electrical signal generatedfrom the target circuit 1102 into the analog electrical signal. Forexample, if the target circuit 1102 is designed to perform a mechanismoperation, such as moving or rotating, in response to a received controleffort, the sensor 1116 is configured to detect the mechanism operationof the target circuit 1102 in order to generate the analog detectionresult to the following ADC 1118. Additionally, if the target circuit1102 is designed to generate an analog electrical signal as its output,the sensor 1116 can be omitted. Similarly, in other embodiments wherethe sensor 1116 is configured to detect operation of the target circuit1102 and then output a digital detection value, the ADC 1118 can beomitted. Briefly summarized, the ADC 1118 and/or the sensor 1116 can beoptional depending upon the design requirements. Those alternativedesigns mentioned above all obey the spirit of the present invention,and therefore fall within the scope of the present invention.

Referring to FIG. 13, the switch 1114 is coupled between the controllingcircuit 1112 and buffers 1106-1, 1106-2, 1106-3, . . . , 1106-N, and isimplemented for coupling the controlling circuit 1112 to the selectedbuffer according to the state decision signal Sd for storing the controldatum to the selected buffer corresponding to the selected operationalstate of the target circuit 1102. Further description of the controlsystem 1100 is as below.

When the target circuit 1102 operates in a first selected operationalstate, state decision circuit 1104 will generate a first state decisionsignal and transmit the first state decision signal to the multiplexer1108. Next, the multiplexer 1108 connects a first buffer correspondingto the first operational state according to the first state decisionsignal and then outputs a first control datum currently saved in thefirst buffer (e.g. the buffer 106-1) to the DAC 1110. Subsequently, theDAC 1110 converts the first control datum into a first analog controlsignal and then outputs the first analog control signal into the targetcircuit 1102. Finally, the target circuit 1102 operates in the firstoperational state according to the first analog control signal.Furthermore, the controlling circuit 1112 will detect the operation ofthe target circuit 1102 and determine a next control datum according toa detecting result. Then, the switch 1114 couples the controllingcircuit 1112 to the first buffer according to the first state decisionsignal received from the state decision circuit 1104 so as to allow thenext control datum to be transmitted from the controlling circuit 1112to the first buffer and thereby be saved in the first buffer.

When it is desired to change operational state in which the targetcircuit 1102 operates from the first selected operational state to asecond selected operational state, the state decision circuit 1104 willgenerate a second state decision signal and transmit the second statedecision signal to the multiplexer 1108. Next, the multiplexer 1108connects a second buffer (e.g. the buffer 1106-2) corresponding to thesecond operational state according to the second state decision signaland then outputs a second control datum currently saved in the secondbuffer to the DAC 1110. Next, the DAC 1110 converts the second controldatum into a second analog control signal and then outputs the secondanalog control signal into target circuit 1102. Finally, the targetcircuit 1102 operates in the second operational state according to thesecond analog control signal, where the transition time required forchanging the target circuit 1102 from the first operational state to thesecond operational state is greatly reduced due to the second controldatum being stored in the second buffer in advance.

Please note that when it is desired to change the operational state inwhich the target circuit 1102 operates from the first selectedoperational state to the second selected operational state, the secondstate decision signal generated by the state decision circuit 1104 willbe delayed by a period of time before being transmitted to the switch1114, for ensuring that a last control datum corresponding to the firstselected operational state is transmitted from the controlling circuit1112 to the first buffer and saved in the first buffer completely beforethe switch 1114 is controlled to establish a connection between thecontrolling circuit 1112 and the second buffer according to the secondstate decision signal received from the state decision circuit 1104.

Briefly summarized, one of the buffers 1106-1, 1106-2, 1106-3, . . . ,1106-N of the control system 1100 is enabled to store a control datumfor a corresponding active operational state of the target circuit 1102,and the control datum is repeatedly updated by the feedback loopestablished by the controlling circuit 1112 before the operational stateof the target circuit 1102 is switched from the selected specific stateto a new state. When the target circuit 1102 re-enters the specificstate, the last control datum, applied to control the target circuit1102 in a previous period when the same specific state is active, isoutput to quickly make an operation of the target circuit 1102 complywith the desired behavior in the specific state. For clear illustration,exemplary embodiments using the multi-buffer architecture are given asbelow. It should be noted that the following exemplary embodiments arefor illustrative purposes only and not meant to be taken as limitationsof the present invention.

FIG. 14 is a diagram illustrating an automatic power control (APC)system 1200 employing the architecture shown in FIG. 13. In thisembodiment, the APC system 1200 is used in an optical disc drive foraccessing a DVD-RAM disc. The APC system 1200 has a laser diode 1240 foremitting laser beams onto an optical disc (i.e. a DVD-RAM disc); asensor 1242 for detecting the laser power of the laser diode 1240; aplurality of state decision circuits 1202, 1212; a playback buffer 1204;a bias buffer 1205; a land buffer 1214; a groove buffer 1215; aplurality of multiplexers 1206, 1216; a plurality of switches 1208,1218; a recording state decision block 1210 for generating a write gatesignal WGATE indicating if the laser diode 1240 enters a write state; aGL decision block 1220 for generating a GL signal indicating a switchingbetween a land track and a groove track on the DVD-RAM disc; a pluralityof digital controllers 1212, 1222; a plurality of ADCs 1214, 1224; aplurality of sample/hold circuits 1216, 1226 for sampling output of thesensor 1242 and holding the sampled values fed into the correspondingADCs 1214; a plurality of DACs 1218, 1228; and a laser driving circuit1230 having a plurality of laser diode drivers 1232, 1234, 1238 for readpower, write power and peak (overdrive) power respectively and a summingcircuit 1238 for summing up driving currents outputted from thepreceding laser diode drivers to drive the laser diode 1240. Since theconfiguration shown in FIG. 14 is created by integrating thearchitecture shown in FIG. 13 into a conventional optical disc drive,and the operations of the optical disc drive are well known to thoseskilled in this art, further description of each component illustratedin FIG. 14 is not detailed here for the sake of brevity. In thefollowing, only the operations pertinent to the disclosed controlmechanism adopted in the APC system 1200 are described.

When it is desired to make the operational state of the optical pick-upunit enter a read state, the state decision circuit 1202 will make themultiplexer 1206 couple with the playback buffer 1204 according to thewrite gate signal WGATE received from the recording state decision block1210, and then the multiplexer 1206 outputs a control effort saved inplayback buffer 1204 as an initial control effort for the read state.Additionally, the state decision circuit 1202 also switches the switch1208 to the playback buffer 1204 after a last control effortcorresponding to the write state is saved completely into the biasbuffer 1205.

On the other hand, when it is desired to make the operational state ofthe optical pick-up unit change to the write state from the read state,the state decision circuit 1202 will make the multiplexer 1206 couplewith the bias buffer 1205 according to the write gate signal WGATEreceived from the recording state decision block 1210, and then themultiplexer 1206 outputs a control effort saved in bias buffer 1205 asan initial control effort for the write state. Additionally, the statedecision circuit 1202 also switches the switch 1208 to the bias buffer1205 after a last control effort corresponding to the read state issaved completely into the playback buffer 1204. Moreover, regarding theDVD-RAM disc recording, the write state of the optical pick-up unit hastwo types, land track state and groove track state. The APC device 1200therefore requires the land buffer 1293 and the groove buffer 1215 forstoring two kinds of control efforts corresponding to the land trackrecording and groove track recording respectively. Accordingly, when theoptical pick-up unit performs a writing operation upon a land track, thestate decision circuit 1252 will make the multiplexer 1295 couple withthe land buffer 1293 according to the indication signal GL received fromthe GL decision block 1220, and then the multiplexer 1295 outputs acontrol effort saved in the land buffer 1293 as an initial controleffort for the land track recording. Additionally, the state decisioncircuit 1252 also switches the switch 1218 to the land buffer 1293 aftera last control effort corresponding to the groove track recording issaved completely into the groove buffer 1215. However, when an end ofthe land track is encountered and the optical pick-up unit is ready torecord data upon a following groove track, i.e. when the optical pick-upunit performs a writing operation upon a groove track, the operations ofthe state decision circuit 1252, multiplexer 1295 and switch 1218 aresimilar to the operations of the state decision circuit 1202,multiplexer 1206 and switch 1208. Therefore, further description isomitted here for brevity.

Please refer to FIG. 13 again. In the control system 1100 of themulti-buffer architecture mentioned above, the control effort stored ina selected buffer of the buffers 1106-1, 1106-2, 1106-3, . . . , 1106-Nwill be applied to the DAC 1110 when the state change occurs. However,due to hardware limitations, there may be an unavoidable latency at theoutput of DAC 1110 while changing the input of the DAC 1110 from controldatum of the current state to control datum of the next state. If thelatency is too large, the overall system performance will be degraded.Commonly, the latency is introduced due to a specific ADC implementationhaving a low-pass filter connected to an output of the analog-to-digitalconverter for stabilizing the analog output fed into the followingcircuit block (e.g. the target circuit 1102). To solve this problem, thepresent invention further discloses a mechanism to dynamically controlthe response speed of the analog output fed into the target circuit1102. Please refer to FIG. 15, which is a block diagram illustrating analternative DAC architecture according to an embodiment of the presentinvention. The DAC 1110 is replaced with the combination including anADC 1110′, a low-pass filter (LPF) 1302, and a filter controller 1304.The ADC 1110′ is used for receiving the control datum outputted from themultiplexer 1108 and then converting the control datum into an analogcontrol signal. The LPF 1302 is implemented for filtering outhigh-frequency components in the analog control signal to smooth theanalog control signal fed into the target circuit 1102. In thisembodiment shown in FIG. 15, the filter controller 1304 is coupled tothe LPF 1302, and is configured to output a control signal BW_SW tochange a bandwidth of the LPF 1302 when detecting a state transitionfrom a selected operational state to a next selected operational state.Please refer to FIG. 16. FIG. 16 is a timing diagram illustrating thefilter bandwidth adjustment controlled by the filter controller 304shown in FIG. 3. Suppose that the target circuit 1102 is a laser diodeof an optical pick-up unit and the current state is a read state. Itshould be noted that the digital-to-analog converter 1110 used in theabove-mentioned embodiments is driven by a fixed clock signal to updateits output periodically according to the input digital value received atthe time triggered by the clock signal. Therefore, as shown in FIG. 16,at the timing Ta0, the DAC 1110′ reads the control datum DACR1 stored ina selected buffer (e.g. the buffer 1106-1) corresponding to the readstate, where the control datum DACR1 is determined by the digitalcontroller 1120 for updating the previous control datum DACR0. At thetiming Ta1 , the operational state of the target circuit 1102 is changedto a write state from the current read state. The filter controller 1304is triggered by the state transition, for example, from the statedecision signal Sd outputted from the state decision circuit 1104, andthe control signal BW_SW is set to a high logic level to switch the LPF1302 to a high bandwidth mode, thereby allowing the analog output of theDAC 1110′ to reach the desired level rapidly. At the timing Ta2, thefilter controller 1304 resets the control signal BW_SW to a low logiclevel to switch the LPF 1302 back to a low bandwidth mode. It should benoted that after the LPF 1302 enters the low bandwidth mode, the analogoutput fed into the target circuit 1102 changes smoothly but thesignal-to-noise ratio (SNR) is high. Similarly, at the timing Ta3, theoperational state of the target circuit 1102 is changed to a read statefrom the current write state. The filter controller 1304 is triggered bythe state transition to make the control signal BW_SW set to a highlogic level to switch the LPF 1302 to a high bandwidth mode, therebyallowing the analog output of the DAC 1110′ to reach the desired levelrapidly; and at the timing Ta4, the filter controller 1304 resets thecontrol signal BW_SW to a low logic level to switch the LPF 1302 back toa low bandwidth mode. In addition, as shown in FIG. 16, the DAC 1110′ isalso configured to change its analog output in spite of the updatingtiming defined by the clock signal inputted thereto. For example, at thetiming Ta1 which is prior to the normal updating timing Ta1′, the DAC1110′ changes its updating timing in response to the state transition;similarly, at the timing Ta3 which is prior to the normal updatingtiming Ta3′, the DAC 1110′ changes its updating timing in response tothe state transition, thereby also decreasing the latency and increasingthe response speed. Any ADC architectures using one or both of theaforementioned latency reduction techniques all fall within the scope ofthe present invention.

Please refer to FIG. 17. FIG. 17 is a block diagram illustrating acontrol system 1300 according to another embodiment of the presentinvention. In this embodiment, the control system 1300 comprises atarget circuit 1302, a state decision circuit 1303, a DAC 1310, abandwidth adjuster 1330, and a controlling circuit 1312 having a sensor1316, an ADC 1318, and a digital controller 1320. Please note that thecomponents of the same name in the embodiments shown in FIG. 13 and FIG.17 have the same operation and functionality, and further description isomitted for brevity. Similarly, the above-mentioned optionalmodifications made to the control system 1100 are suitable for thecontrol system 1300, and further description is omitted here as well.The bandwidth adjuster 1330 is coupled to the digital controller 1320and the state decision circuit 1303 to adjust the bandwidth of thecontroller according to the state decision signal Sd generated from thestate decision circuit 1303. For example, the bandwidth adjuster 1330 isconfigured to change the bandwidth of the digital controller 1320 from afirst bandwidth to a second bandwidth higher than the first bandwidthwhen a state transition occurs, and then change the bandwidth of thedigital controller 1320 from the second bandwidth to the first bandwidthafter a predetermined period of time.

In this embodiment, the bandwidth adjuster 1330 adjusts the bandwidth ofthe digital controller 1320 by adjusting a gain setting of the digitalcontroller 1320, a clock rate of the digital controller 1320, or acombination thereof. For example, suppose that the digital controller1320 is operated under a clock rate CLK and is configured to have a gainG, where the clock rate CLK defines the updating speed of the analogoutput, and the gain G defines the step size of adjusting the analogoutput. If the clock rate CLK is doubled to be 2*CLK with the same gainG, the time required for changing the analog output from a first levelto a second level is half that of the original bandwidth setting;similarly, if the gain G is doubled to be 2*G and the clock rate CLK isunchanged, the time required for changing the analog output from thefirst level to the second level is also half that of the originalbandwidth setting. For clear illustration, exemplary embodiments usingthe bandwidth adjuster are given as below. It should be noted that thefollowing exemplary embodiments are for illustrative purposes only andnot meant to be taken as limitations of the present invention.

FIG. 18 is a diagram illustrating an automatic power control (APC)system 1600 employing the architecture shown in FIG. 17, and FIG. 19 isa diagram illustrating another automatic power control (APC) system 1700employing the architecture shown in FIG. 17. In these embodiments, theAPC systems 1600 and 1700 each are used in an optical disc drive foraccessing a DVD-RAM disc. Since the operation and functionality of thecomponents having aforementioned reference numerals are detailed above,further description is omitted here for brevity. In FIG. 18, themulti-gain generator 1602 serves as a bandwidth adjuster used forsetting the gain setting of the corresponding digital controller 1212 bya target gain value selected from the candidate gain values G1, G2, . .. , GN to thereby adjust the controller bandwidth, and the multi-gaingenerator 1604 serves as a bandwidth adjuster used for setting the gainsetting of the corresponding digital controller 1222 by a target gainvalue selected from the candidate gain values G1′, G2′, . . . , GN′ tothereby adjust the controller bandwidth. Regarding the APC system 1700shown in FIG. 7, the multi-frequency generator 1702 serves as abandwidth adjuster used for setting the clock rate of the correspondingdigital controller 1212 by outputting a clock signal with a targetfrequency selected from the candidate clock signals with differentfrequency values F1, F2, . . . , FN to thereby adjust the controllerbandwidth, and the multi-frequency generator 1704 serves as a bandwidthadjuster used for setting the clock rate of the corresponding digitalcontroller 1222 by a clock signal with a target gain value selected fromthe candidate clock signals with different frequency values F1′, F2′, .. . , FN′ to thereby adjust the controller bandwidth. It should be notedthat the disclosed ADC architecture in FIG. 15 can be applied to the APCsystems 1600, 1700 to reduce the latency of changing the analog outputfed into the following target circuit (e.g. the laser diode of theoptical pick-up unit). This also falls within the scope of the presentinvention.

Please refer to FIG. 20. FIG. 20 is a schematic diagram of an APC system2502 coupled to the OPU 2405 according to an embodiment of the presentinvention. The APC system 2502 is utilized for controlling an outputpower level emitted from the OPU 2405. The APC system 2502 furtherutilizes a peak power control circuit 2505 and a DAC 2510 forcontrolling an actual peak power level emitted from the LD D1 at atarget peak power level. In this embodiment, suppose that an actualwrite power level and an actual read power level emitted from the LD D1have been calibrated at a target write power level Pw and a target readpower level Pr respectively. The peak power control circuit 505 isutilized for receiving a write power control value outputted from thewrite power control circuit 2435 and then determining a peak powercontrol value according to the target write power level Pw, the targetread power level Pr, the target peak power level Ppk, and the receivedwrite power control value. The peak power control value is amplified bya digital gain amplifier GRATIO X′ times, which X′ means a value equalto (Ppk−Pw)/Pw; the amplified peak power control value is then convertedinto a driving signal Spk by the DAC 2510. The driving signal Spk isamplified through the adjustable gain amplifier GPK_ADJ and the gainamplifier GPK_LDD for outputting a driving signal Spk′ to the analogadder Gsum. The analog adder Gsum can output a resultant driving signalto drive the LD D1 for irradiating an appropriate power level onto arecordable disc according to the driving signals Sr′, Sw′, and Spk′. Forexample, the driving signals Sr′, Sw′, and Spk′ are all non-zero drivingcurrents when the multiplexers MUX1, MUX2, and MUX3 are controlledrespectively by signals EN_R, EN_W, and EN_PK to remain in state S1. Theanalog adder Gsum can sum up the driving currents Sr′, Sw′, and Spk′ tooutput the resultant driving current fed into the LD D1 for driving theLD D1 to emit a laser light with the target peak power level Ppk. Thedetailed operation of the peak power control circuit 505 is discussed inthe following paragraphs.

Please refer to FIG. 21. FIG. 21 is a diagram showing a straight line SLand a characteristic curve CV of the LD D1 shown in FIG. 20. It isassumed that a slope of the characteristic curve CV from the target readpower level Pr to the target write power level Pw is identical to thatof the characteristic curve CV from the target write power level Pw tothe target peak power level Ppk, and the slope is also identical to thatof the straight line SL extending from the characteristic curve CV. Theslope is also considered as a total gain of a driving current to anoutput power and referred to as Gw in this embodiment. As shown in FIG.21, the straight line SL crosses the horizontal axis at a point I1(representative of a current value) on the horizontal axis, and theslope Gw can be calculated according to the target read power level Pr,the target write power level Pw, and an amount of current ΔIw′corresponding to the write power control value. According to thewell-known equal ratios theorem, a ratio of an amount of current ΔI1′ toan amount of current ΔI1 is identical to that of a power difference ΔP1(this is equal to the target write power level Pw) to a power differenceΔP2, where the power difference ΔP2 is equal to the target peak powerlevel Ppk. This relation can be illustrated by the following equation:

$\begin{matrix}{\frac{P_{w}}{P_{p\; k}} = {\frac{\Delta\; I_{1}^{\prime}}{\Delta\; I_{1}} = \frac{( {{\Delta\; I_{1}^{''}} + \Delta_{w}^{\prime}} )}{( {{\Delta\; I_{1}^{''}} + {\Delta\; I_{w}^{\prime}} + {\Delta\; I_{p\; k}^{\prime}}} )}}} & {{Equation}\mspace{14mu}(1)}\end{matrix}$

In Equation (1), the parameter ΔI1″ is meant to be an amount of currentshown in FIG. 21 and can be calculated according to the slope Gw andtarget read power level Pr, and the amount of currentΔIw′ can be derivedaccording to the driving signal Sw′. Since the target peak power levelPpk and the target write power level Pw are known and the amounts ofcurrent ΔI1″ and ΔIw′ are calculated, the amount of current ΔIpk′ canalso be calculated by Equation (1). That is, the peak power controlvalue can be derived if the write power control value and an adjustingvalue corresponding to the amount of current ΔI1″ are determined, sincea conversion relation between driving signals corresponding to theabove-mentioned amounts of current and control values is almost linear.Thus, the adjusting value corresponding to the amount of currentΔI1″ canbe calculated according to the amount of current ΔI1″ and the conversionrelation between the driving signals and control values. The peak powercontrol value is determined once the adjusting value is calculated, andthen the APC system 2502 can control the actual peak power level at thetarget peak power level Ppk correctly according to the peak powercontrol value. In this embodiment, the peak power control value is equalto the value of the write power control value plus the determinedadjusting value. Even though a required driving current passing throughthe LD D1 may be a little different due to the above-mentioned reasons(e.g. a change of the temperature of the LD D1 or the other factors),the APC system 2502 can still control the actual peak power level at thetarget peak power level Ppk effectively by deriving a new adjustingvalue according to the target read power P

r, and a new calculated slope (usually, when the required drivingcurrent is different, there is also some possibility that the writepower control value is changed and therefore it is necessary tocalculate a new slope).

The new slope can be calculated according to the target read power levelP

r, the target write power level Pw, and the changed write power controlvalue.

In addition, since the slope Gw of the characteristic curve CV from thetarget read power level Pr to the target write power level Pw is assumedto be identical to that of the characteristic curve CV from the targetwrite power level Pw to the target peak power level Ppk, it is alsonecessary to adjust the gain of the adjustable gain amplifier GPK_ADJ toensure that the gain of the write channel is equal to that of a peakchannel. The peak channel is meant to be a signal path through the peakpower control circuit 2505, the digital gain amplifier GRATIO, the DAC2510, the adjustable gain amplifier GPK_ADJ, and the gain amplifierGPK_LDD. Therefore, the relation between total gains of the writechannel and the peak channel can be illustrated as the followingequation:X′×G _(pkadj) ×G _(pkldd) ×G _(s) =G _(wadj) ×G _(wldd) ×G_(s)  Equation (2)

In Equation (2), the parameter X′ is just the ratio (Ppk−Pw)/Pw.Parameters Gpkadj, Gpkldd, Gwadj, Gwldd, and Gs are gains of the gainamplifiers GPK_ADJ, GPK_LDD, GW_ADJ, GW_LDD, Gsum respectively. FromEquation (2), the gain Gpkadj of the adjustable gain amplifier GPK_ADJcan be determined since the gain Gpkadj depends on the parameters R,Gpkldd, Gwadj, and Gwldd.

Of course, it will be obvious that the gains Gpkadj and Gwadj are thesame and the adjustable gain amplifiers GPK_ADJ and GW_ADJ can thereforebe removed from the APC system 2502 without incurring errors if thegains Gpkldd and Gwldd are identical and the target write power level Pwis half of the target peak power level Ppk. In another embodiment, theamount of current ΔIpk′ corresponding to the peak power control valuecan equivalently be derived by directly dividing the target write powerlevel Pw by the slope Gw, without calculating the amount of current ΔI1″corresponding to the adjusting value. That is, the peak power controlcircuit 2505 can also generate the peak power control value according tothe target write power level Pw and the slope Gw, without calculatingthe adjusting value. This also falls within the scope of the presentinvention.

Furthermore, although controlling the actual peak power level at thetarget peak power level when accessing/recording a recordable disc isonly discussed in the above-mentioned embodiments, the method disclosedin the embodiments of the present invention can also be applied tocontrolling an actual write power level at a target write power levelwhen accessing/recording a rewritable disc. This also obeys the spiritof the present invention.

In other embodiments, the peak power control circuit 2505 can furthermultiply the above-mentioned peak power control value by the parameterX′ (i.e. the ratio (Ppk−Pw)/Pw) to output an amplified control value tothe DAC 2510. Thus, the digital gain amplifier GRATIO in the APC system2502 is not required and is excluded from the APC system 2502. Therelation between total gains of the write channel and the peak channelis illustrated as the following equation:G _(pkadj) ×G _(pkldd) ×G _(s) =G _(wadj) ×G _(wldd) ×G _(s)  Equation(3)

Referring to Equation (3), the gain Gpkadj of the adjustable gainamplifier GPK_ADJ only depends on the parameters Gpkldd, Gwadj, andGwldd.

Moreover, in another embodiment, the adjustable gain amplifiers GR_ADJ,GW_ADJ, and GPK_ADJ can be respectively replaced by other digitaladjustable gain amplifiers, which are located at the front stages of theabove-mentioned power control circuits(as shown in FIG. 22). In thisembodiment, the gain of an adjustable gain amplifier GPK_ADJ′ ismodified as the original gain value (i.e. the gain of the adjustablegain amplifier GPK_ADJ in the APC system 2502) multiplied by theabove-mentioned parameter X′. Consequently, the digital gain amplifierGRATIO is not needed. However, the gain of the adjustable gain amplifierGPK_ADJ′ can also be designed to be equal to the gain of the adjustablegain amplifier GPK_ADJ in the APC system 2502, so the digital gainamplifier GRATIO is required in this situation. This also obeys thespirit of the present invention.

FIG. 23A is a flowchart of a first method of generating a zero crossingsignal of an optical disc drive according to an embodiment of theinvention. The method comprises receiving at least a digital servosignal of the optical disc drive (step S11). The digital servo signalfrom the optical disc drive can be a tracking error (TE) signal, a radiofrequency ripple (RFRP) signal, a focus error (FE) signal or other.Next, new data is interpolated between every two adjacent digital servosignals which cross zero (step S12). Finally, a servo zero crossingsignal is generated through the interpolated data (step S13).

FIG. 23B is a flowchart of a second method of generating a zero crossingsignal of an optical disc drive according to another exemplaryembodiment of the invention. First, at least a first digital servosignal of the optical disc drive is received (step S21). Also, thedigital servo signal from the optical disc drive can be a tracking error(TE) signal, a radio frequency ripple (RFRP) signal, a focus error (FE)signal or other. Next, the first digital servo signal data is upsampledto generate a second digital servo signal with higher resolution thanthe first digital servo signal (step S22). Finally, a servo zerocrossing signal is generated by slicing the second digital servo signal(step 23).

FIG. 24 shows a signal processing apparatus 3400 for an optical discdrive (not shown in FIG. 24) according to an exemplary embodiment of theinvention. Optical pickup unit (OPU) 3401 of the optical disc drivereceives a laser signal reflected from a disc and generates signals A toH which are sent to a preprocessing block 3402. Here, the preprocessingblock 3402 is a circuit block as shown in FIG. 1, which performs sampleand hold (S/H) operation, gain and offset adjustments, and outputssignals ASH to HSH to an analog-to-digital conversion (ADC) device 3403.In FIG. 24, the analog-to-digital conversion device 3403, comprising ananalog-to-digital (A/D) converter 3403 a and a signal converter 3403 b,converts the signals ASH to HSH to servo signals comprising a digitaltrack error (TE) signal, a digital radio frequency ripple (RFRP) signal,a digital focus error (FE) signal and other digital servo signals (notshown in FIG. 24). A reshaping device 3404 receives the digital TEsignal, digital RFRP signal and digital FE signal, generating a new TEsignal TE′, new RFRP signal RFRP′ and new FE signals FE′ for the servocontrol-and-detection device 2406.

The signal processing aparatus 3400 operates in conjunction with thefirst method shown in FIG. 3A. Thus, the reshaping device 3404 of thesignal processing apparatus 3400 receives the digital TE signal, RFRPsignal and FE signal, for example, and interpolates new data betweenevery two adjacent digital servo signals (or data) which cross zero. Inthis embodiment, new data is merely interpolated to the digital TEsignal to generate the interpolated TE signal TE′, although thedisclosure is not limited thereto. Then, the servo control-and-detectiondevice 3406 generates a TEZC signal (not show in FIG. 24) through theinterpolated data to perform further servo control and detection.

FIG. 25 shows generation of the TEZC signal based on the first method ofFIG. 3A. Signals TEA and TEZCA, represent waveforms of an analog TEsignal and an ideal TEZC signal sliced from the analog TE signal. TED1and TEZCD1 represent waveforms of the digital TE signal and the TEZCsignal generated through or sliced using the interpolated data. Theblock circles 58 in the TED1 signal are samples taken by theanalog-to-digital conversion device 3403 using a first sampling rate.The sampling rate corresponds to the frequency of a first clockgenerator 3407. In FIG. 25, the reshaping device 3404 interpolates data51 to 53 between every two adjacent digital TED1 signal data which crosszero to generate the TE′ signal depicted as a dotted line in FIG. 25.Then, the servo control-and-detection device 2406 slices the digital TE′signal through the interpolated data 51 to 53 to generate the TEZCD1signal. It can be seen from FIG. 25 that the TEZCD1 signal is moreaccurate than the TEZC signal TEZCD (as a dotted line 55 in FIG. 25). Inthis embodiment, only one new data is interpolated between two adjacentdigital TE signal data which cross zero, but the disclosure is notlimited thereto. A plurality of data can be interpolated between twoadjacent digital TE signal data which cross zero, and that closest tozero can be selected to slice the interpolated TE signal TE′.

Signal processing apparatus 3400 also can operate in conjunction withthe second method shown in FIG. 23B. Accordingly, the reshaping device3404 of the digital servo signal generator 400 receives the digital TEsignal, RFRP signal and FE signal, and upsamples the digital TE, RFRPand FE signal data to generate the upsampled digital TE, RFRP and FEsignals (TE′, RFRP′ and FE′), all with higher resolution than thedigital TE, RFRP and FE signals. Then, the servo control-and-detectiondevice 3406 generates at least one zero crossing signal of the TE′,RFRP′ and FE′ signals (all not show in FIG. 24) through thecorresponding upsampled signal to perform further servo control anddetection. It is noted that the reshaping device 3404 can be a resamplecircuit, with the signal processing apparatus 3400 further comprising afilter 3405 coupled between the resample circuit of the reshaping device3404 and the servo control-and-detection device 3406. For example, thefilter 3405 can be a second order finite impulse response (FIR) filterwhich may be an interpolation filter with FIR structure ofY(n)=x(n)/2+x(n−1)/2, but the disclosure is not limited thereto.

FIG. 26 shows generation of the TEZC signal based on the second methodof FIG. 3B. Signals TEA1 and TEZCA1 represent waveforms of an analog TEsignal and an ideal TEZC signal sliced from the analog TE signal.Signals TED1 and TE′ represent waveforms of the digital TE signal andthe reshaped (upsampled or resampled) TE signal. Signal TEZC′ is theTEZC signal generated from the TE′ signal. If sampling rate of the TED1signal is 100 KHz, when track speed is about 5 KHz, the ADC device 3403will sample 5 points for one whole period, as shown in signal TED1. Inthis embodiment, for example, the reshaping device (or resample circuit)3404 upsamples the TED1 to 200 KHz and sends the upsampled TED1 signalto the filter 3405, thereby obtaining the reshaped TE signal TE′ whichis smoother and has 20 data points in one period, as depicted in FIG.26. The reshaped TE signal TE′ has a higher resolution than the digitalTE signal TED1. Then, the servo control-and-detection device 3406 slicesthe reshaped TE signal TE′ to generate the TEZC′ signal with higherresolution than the TEZCD signal sliced from the digital TE signal TED1.Numerals 60 and 62, depicted by the dashed line in FIG. 26, indicatepossible width deviations. It can be seen from FIG. 26 that the possiblewidth deviation of the TEZC′ signal is less than that of the TEZCD1signal. Use of the TEZC′ signal for further servo control and detection,such as short seek velocity control, provides better performance.

It is noted that the analog-to-digital conversion (ADC) device 3403,clocked by a first clock generator 3407, couples and processes signals Ato H to generate the digital TE signal of a first sampling rate. Thereshaping device 3404, filter 3405 and servo control-and-detectiondevice 3406, all clocked by a second clock generator 3408 with higherfrequency than the first clock generator 3407, have a higher dataprocessing rate than the first sampling rate of the ADC device.

FIG. 27 shows another signal processing apparatus 3700 for an opticaldisc drive (not shown in FIG. 27) according to another embodiment of theinvention. Optical pickup unit (OPU) 3701 of the optical disc drivereceives laser signal from disc and generates signals A to H which aresent to preprocessing block 3702. In FIG. 7, the main-beam summationmodule 402 is an analog block which processes signals A to H and outputsservo signals comprising at least an analog track error (TEa) signal, ananalog radio frequency ripple (RFRPa) signal, an analog focus error(FEa) signal and other analog servo signals (not shown in FIG. 27).Servo signals are sent to an analog-to-digital conversion (ADC) device3703 to generate digital servo signals such as a digital TE signal, adigital RFRP signal, a digital FE signal and other digital servo signals(not shown in FIG. 27). The reshaping device 3704 receives and processesthe digital servo signals in conjunction with the first method of FIG.23A or the second method of FIG. 23B. The reshaping device 3704 in FIG.27 and the reshaping device 3404 in FIG. 24 have the same functions,corresponding to the same waveforms shown in FIGS. 25 and 26. Thereshaping device 3704 can be a resample circuit. A filter 3705 coupledbetween the reshaping device 3704 and the servo control-and-detectiondevice 3706 can be, for example, a second order finite impulse response(FIR) filter which may be an interpolation filter with FIR structure ofY(n)=x(n)/2+x(n−1)/2, but the disclosure is not limited thereto.

It is noted that the servo control-and-detection device in FIGS. 34 and37 can be implemented using a digital signal processing (DSP) device.

FIG. 28 shows a servo system for an optical disc drive according toanother exemplary embodiment of the invention, wherein detailed blockdiagrams of a reshaping device and a servo control-and-detection devicewhich may be applied in the above embodiments are shown. In thisexample, the reshaping device 3804 comprises two resample circuits 3804a and 3804 b, respectively receiving a digital TE signal and a digitalRFRP signal. The resample circuits 3804 a and 3804 b operate based onthe first method of FIG. 23A or the second method of FIG. 23B,outputting interpolated or upsampled digital TE signal and digital RFRPsignal. Filters 3805 a and 3805 b further smooth the interpolated orupsampled digital TE signal and digital RFRP signal, to output TE′signal and RFRP′ signal. A servo control-and-detection device 3806slices the TE′ signal and the RFRP′ signal by comparators 3806 a and3806 b to generate a TEZC′ signal and a RFRP′ signal. A seek controlmodule 3806 c of the servo control-and-detection device 806 performsseek control for an optical disc drive. In this example in FIG. 28, theADC device 3803 is clocked by a first clock generator 3807 with afrequency of 100 KHz, the resample circuit 804 a and filter 3805 a areclocked by a second clock generator 3808 with a frequency of 200 KHz,and the resample circuit 3804 b and filter 3805 b are clocked by a thirdclock generator 3809 with a frequency of 200 KHz. Therefore, the dataprocessing rates of the resample circuits 3804 a and 3804 b, and filters3805 a and 3805 b are higher than the sampling rate of the ADCconverter.

In view of the above embodiments, the servo zero crossing signal such asTEZC and RFZC signals have reduced width deviations, thereby providingimproved waveform accuracy, enabling servo systems to achieve betterperformance in servo control and detection using the TEZC and RFZCsignals or others obtained according to embodiments of the invention.

FIG. 4 shows a signal processing apparatus 4400 of an optical disc driveaccording to an embodiment of the invention. The signal processingapparatus 4400 comprises an analog circuit 4402, an analog-to-digitalconversion (ADC) device 4403 and a high pass filter (HPF) 4404. Theanalog circuit 4402 receives a laser signal from a disc in the opticaldisc drive (not shown in FIG. 29) to generate servo signals. The ADCdevice 4403, for example an analog-to-digital (A/D) converter, receivesthe servo signals and generates digital servo signals such as digitaltracking error (TE) signal, digital radio frequency ripple (RFRP)signal, digital focus error (FE) signal and others. The HPF 4404 mayreceive at least one of the servo signal Ds, such as the TE signal, tooutput a high pass filtered signal SC for subsequent generation of aservo control signal.

The HPF 4404 comprises a first low pass filter (LPF) 4404 a of a firstsampling rate, receiving and filtering the digital servo signal Ds, adown-sampler 4404 b receiving a first filtered signal output by thefirst LPF 4404 a to down-sample the first filtered signal by a factor Nof integer; a second LPF 4404 c of a second sampling rate, receiving andfiltering a first down-sampled signal output by the down-sampler 4404 b,wherein the second sampling rate is equal to 1/N times the firstsampling rate; an up-sampler 4404 d receiving a second filtered signaloutput by the second LPF 4404 c to up-sample the second filtered signalby the factor N; and a subtractor (or an adder) 4404 e subtracting anup-sampled signal Sup output by the up-sampler 4404 d from the digitalservo signal Ds.

In this embodiment, the ADC device 4403 and the first LPF 4404 a areclocked or synchronized by a clock generator 4405 of clock rate (orfrequency) CK1. Therefore, the first sampling rate of the first LPF 4404a is CK1, and the ADC device 4403 samples the servo signals by the firstsampling rate CK1. A frequency divider 4406 divides clock signal of theclock generator 4405 by the factor N, and outputs a divided clock signalof clock rate CK2 (equal to

$\frac{{CK}\; 1}{N} \quad )$to the second LPF 4404 c. Therefore, the second sampling rate of thesecond LPF 4404 c is CK2. It is noted that the first LPF 4404 a can bean anti-alias filter for the second LPF, and the second LPF 4404 c isdesigned to have a low corner frequency corresponding to the desiredfrequency (or bandwidth) of the HPF 4404. In addition, both the firstand second LPFs 4404 a and 4404 c can have unit DC gain. In order to notlose bit information, two cascade-coupled LPFs implement the HPF,according to this embodiment. Therefore, a high pass filter with a lowerfrequency (or bandwidth) is obtained without losing too much bitinformation.

FIG. 30 shows a signal processing apparatus 4500 of an optical discdrive according to another embodiment of the invention. The signalprocessing apparatus 4500 comprises an analog circuit 4502, ananalog-to-digital conversion (ADC) device 4503 and a high pass filter(HPF) 4504. The analog circuit 4502 receives a laser signal from a diskin the optical disc drive (not shown in FIG. 30) to generate servosignals. The ADC device 4503, for example an analog-to-digital (A/D)converter, receives the servo signals and generates digital servosignals such as tracking error (TE) signal, radio frequency ripple(RFRP) signal, focus error (FE) signal and others. The HPF 4504 mayreceive at least one of the servo signals Ds, such as the TE signal, tooutput a high pass filtered signal SC for subsequent generation of aservo control signal.

The HPF 4504 comprises a first low pass filter (LPF) 4504 a of a firstsampling rate, receiving and filtering the digital servo signal; a firstdown-sampler 4504 b receiving a first filtered signal output by thefirst LPF 4504 a to down-sample the first filtered signal by a factor Nof integer; a second LPF 4504 c of a second sampling rate, receiving andfiltering a first down-sampled signal output by the first down-sampler4504 b, wherein the second sampling rate is equal to 1/N times the firstsampling rate; a second down-sampler 4504 f receives a second filteredsignal output by the second LPF 4504 c to down-sample the secondfiltered signal by a factor M of integer; a third LPF 4504 g of a thirdsampling rate, receiving and filtering a second down-sampled signaloutput by the second down-sampler 4504 f, wherein the third samplingrate is equal to 1/M times the second sampling rate; an up-sampler 4504d receiving a third filtered signal output by the third LPF 4504 g toup-sample the third filtered signal by a factor N×M; and a subtractor(or adder) 4504 e subtracting an up-sampled signal Sup output by theup-sampler 4504 d from the digital servo signal Ds.

In this embodiment, the ADC device 4503 and the first LPF 4504 a areclocked or synchronized by a clock generator 4505 of clock rate CK1.Thus, the first sampling rate of the first LPF 4504 a is CK1, and theADC device 4503 samples the servo signals using the first sampling rateCK1. A first frequency divider 4506 divides clock signal of the clockgenerator 4505 by the factor N, and outputs a divided clock signal ofclock rate CK2 (equal to

$\frac{{CK}\; 1}{N} \quad )$to the second LPF 4504 c. A second frequency divider 4507 divides clocksignal output from the first frequency divider 4506 by the factor M, andoutput a divided clock signal of clock rate CK3 (equal to

$\frac{{CK}\; 2}{M} \quad )$to the third LPF 4504 g. Therefore, the second and third sampling rateof the second and third LPFs 4504 c and 4504 g are CK2 and CK3respectively. It is noted that the first and second LPF 4504 a and 4504c can be anti-alias filters, and the third LPF 4504 g is designed tohave a low corner frequency corresponding to the desired frequency (orbandwidth) of the HPF 4504. In addition, the first to third LPFs 4504 a,4504 c and 4504 g can have unit DC gains. A low corner frequency needs asmall coefficient for a LPF. In order to not lose bit information, threecascade-coupled LPFs are used to implement the HPF, according to thisembodiment. Thus, a high pass filter with a lower frequency (orbandwidth) is obtained, without losing too much bit information.

To be compatible with a general HPF structure, the HPF 4404 of thesignal processing apparatus 4400 can be modified to further comprise aselector, as shown in FIG. 31. The selector 4602 selectively couples theup-sampled signal Sup or the first filtered signal Sf1 to the subtractor4404 e according to the desired frequency (or bandwidth) of the HPF4404. If the desired frequency of the HPF 4404 exceeds a thresholdfrequency, the selector 4602 bypasses the down-sampler 4404 b, thesecond LPF 4404 c and the up-sampler 4404 d to couple the first filteredsignal Sf1 to the subtractor 4404 e. Therefore, the HPF 4404 outputs thefiltered signal SC=Ds−Sf1. Otherwise, the selector 4602 couples theup-sampled signal Sup to the subtractor 4404 e. Therefore, the HPF 4404outputs the filtered signal SC=Ds−Sup. In this embodiment, the digitalservo apparatus may comprise a control module (not shown in FIG. 31). Inthe flowchart of FIG. 32, the control module determines if the desiredHPF frequency exceeds the threshold frequency (Step S41). The controlmodule controls the selector 4602 to output the up-sampled signal Sup tothe subtractor 4404 e, and sets the corner frequency fc2 of the secondLPF to the desired frequency fd of the HPF 4404 and sets the cornerfrequency fc1 of the first LPF to a multiple of desired frequency fd,m×fd, when the desired frequency of the HPF 4404 does not exceed thethreshold (Step S42). The control module controls the selector 4602 tooutput the first filtered signal Sf1 to the subtractor 4404 e and setthe corner frequency fc1 of the first LPF to the desired frequency fd ofthe HPF 4404 when the desired frequency of the HPF 4404 exceeds thethreshold (Step 43).

It is noted that the selector can also be applied to the HPF disclosedin FIG. 30 in conjunction with the control module, according toflowchart of FIG. 32.

FIG. 33 shows a signal processing apparatus of an optical disc driveaccording to another embodiment of the invention, wherein a high passfilter of the signal processing apparatus is implemented using twocascade-coupled low pass filters. In the signal processing apparatus ofFIG. 33, a digital TE signal is first filtered by a high pass filter toremove DC component thereof, and then the filtered TE signal is slicedby a comparator to generate a tracking error zero crossing (TEZC) signalfor subsequent servo control of the optical storage system. Opticalpickup head (PUH) 801 of the optical storage system (not shown in FIG.33) receives a laser signal from a disc and generates signals A to Hwhich are sent to a preprocessing block 4802. Here, the preprocessingblock 4802 is a circuit block which performs sample and hold (S/H)operation, gain and offset adjustments, and outputs signals ASH to HSHto an analog-to-digital conversion (ADC) device 4803. In FIG. 33, theanalog-to-digital conversion device 4803, comprising ananalog-to-digital (A/D) converter 4803 a and a signal converter 4803 b,converts the signals ASH to HSH to servo signals comprising a digitaltrack error (TE) signal, a digital radio frequency ripple (RFRP) signal,a digital focus error (FE) signal and other digital servo signals. Here,only the digital TE signal is shown in FIG. 33. The digital TE signal issent to a high pass filter (HPF) 4804 to remove DC component thereof.Then, the filtered TE signal TEHPF is sliced by a comparator 808 togenerate a tracking error zero crossing (TEZC) signal.

In this embodiment, the HPF 4804 comprises a first low pass filter (LPF)4804 a, a down-sampler 4804 b, a second LPF 4804 c, an up-sampler 4804d, a selector 4804 f and a subtractor (or adder) 4804 e. The first LPF804 a, with a first sampling rate CK1, receives and filters the digitalTE signal. A clock generator 4805 provides clock signal CK1 withfrequency 3 MHz to the ADC device 4803, the first LPF 4804 a and afrequency divider 4806. Thus, the first sampling rate of the LPF 4804 ais 3 MHz.

The down-sampler 4804 b receives a first filtered TE signal todown-sample the first filtered signal by a factor N of integer. Forexample, N is equal to 12. The second LPF 4804 c of a second samplingrate, receives and filters a down-sampled signal output by thedown-sampler 4804 b. The frequency divider 4806 divides the clock signalCK1 by the factor 12 and generates a divided clock signal CK2 of 250 KHzto the second LPF 4804 c. Thus, the second sampling rate is equal to1/12 times the first sampling rate, i.e. 250 KHz. The up-sampler 4804 dreceives a second filtered signal output by the second LPF 4804 c toup-sample the second filtered signal by the factor 12.

The selector 4804 f selectively couples the up-sampled signal Sup or thefirst filtered signal Sf1 to the subtractor 4404 e according to thedesired frequency (or bandwidth) of the HPF 4804. If the desiredfrequency of the HPF 804 exceeds a threshold frequency, the selector4602 bypasses the down-sampler 4804 b, the second LPF 4804 c and theup-sampler 4804 d to couple the first filtered signal Sf1 to thesubtractor 4404 e. Otherwise, the selector 804 f couples the up-sampledsignal Sup to the subtractor 4404 e. In this embodiment, the signalprocessing apparatus 4800 may comprise a control module (not shown inFIG. 33). The operations of the control module in conjunction with theselector 4804 f are similar to those described in FIG. 32. First, thecontrol module determines if the desired HPF frequency exceeds thethreshold frequency (Step S41). The control module controls the selector4804 f to output the up-sampled signal Sup to the subtractor 4804 e, andsets the corner frequency fc2 of the second LPF to the desired frequencyfd of the HPF 4804 and the corner frequency fc1 of the first LPF to N×fdwhen the desired frequency of the HPF 804 does not exceed the threshold(Step S42). On the contrary, the control module controls the selector4804 f to output the first filtered signal Sf1 to the subtractor 4804 eand sets the corner frequency fc1 of the first LPF to the desiredfrequency fd of the HPF 4804 when the desired frequency of the HPF 4404exceeds the threshold (Step 43).

Table B shows examples of different bandwidths, coefficients, and lostbits when implementing a HPF using only one LPF. Coefficients of the lowpass filters in table B are shown in decimal and hexadecimal fixed pointQ15 formats. It is clear that the smaller the coefficient (the LPFfrequency), the more bits are lost. The HPF implemented by only the LPFsuffers serious limitation of precision when requiring lower HPFfrequency (i.e., lower LPF corner frequency).

TABLE B LPF Frequency Coefficient (Dec.) Coefficient (Hex) Lost Bits 18KHz 0.03699 4BC 4 14 KHz 0.02970 3CE 5 8 KHz 0.01496 1EA 6 4 KHz 0.00751F6 7 2 KHz 0.00401 84 8 1 KHz 0.00200 42 9 500 Hz 0.00100 21 10

Assume the first and second LPFs 4804 a and 4804 c are IIR LPFs, thesampling rates of the first and second LPFs are 3 MHz and 250 KHz, andthe first LPF is an anti-alias filter, Table C shows lost bit numbers ofHPFs (4804) with different desired bandwidths (BW) implemented accordingto disclosure of FIG. 33. Here, the threshold frequency is 2 KHz. Asdescribed in FIG. 33, when the desired HPF frequency exceeds 2 KHz, theselector 4804 e bypasses the second LPF 4804 c and the up-sampler 4804d, and the corner frequency of the first LPF is set to the desired HPFfrequency. In addition, when the desired HPF frequency fd does notexceed 2 KHz, the HPF 4804 is implemented by the two cascade-coupledLPFs 4804 a and 4804 c, and the corner frequency of the second LPF isset to the desired HPF frequency fd.

TABLE C Desired HPF BW 1st LPF (804a) 2nd LPF (804c) Total Lost Bits 250Hz 8K 250 Hz 6 500 Hz 8K 500 Hz 5 1 KHz 14K   1 KHz 4 2 KHz 18K   2 KHz3 4 KHz 4K Bypass 7 8 KHz 8K Bypass 6 16 KHz 16K  Bypass 5 18 KHz 18K Bypass 4

Comparing the lost bit numbers in table B and table C, when the desiredHPF frequency is within 250 Hz to 2 KHz, it is clear that the lost bitnumbers are reduced using the HPF based on FIG. 33.

Please refer to FIG. 34. FIG. 34 is a block diagram illustrating anexemplary embodiment of an apparatus 5100 capable of determining areference level according to an input signal and a reference signal andthen processing the input signal using the determined reference level.In this embodiment, the apparatus 5100 is designed to operate in adigital domain. That is, the apparatus 5100 is a digital circuit.However, this is not meant to be a limitation of the present invention.After reading following descriptions, a person skilled in this art wouldunderstand that other implementations obeying the spirit of the presentinvention are possible. Additionally, in the following embodiments theinput signal is the aforementioned RFRP signal, the reference signal isthe aforementioned TEZC signal, and the reference level is a slicerlevel used for slicing the RFRP signal to generate a sliced signal,i.e., the aforementioned mirror signal. Similarly, this is not meant tobe a limitation of the present invention.

As shown in FIG. 34, the apparatus 5100 comprises a high-pass filter(HPF) 5102, a detecting circuit 5104, a decision 5106, an updatecontroller 5108, a protection circuit 5110, an initial value controller5112, and a comparator 5114. The HPF 5102 is used for filtering out DCcomponents of the incoming input signal (e.g., an RFRP signal) Sin toremove the DC offset; however, it is an optional circuit componentdepending upon design requirements. The detecting circuit 5104 isconfigured to detect a target peak value and a target bottom value ofthe RFRP signal Sin within at least one period of a reference signal(e.g., a TEZC signal) Sref. For example, in this embodiment, thedetecting circuit 5104 detects the peak value and the bottom value perperiod of the TEZC signal Sref.

As shown in FIG. 34, the detecting circuit 104 includes an edge trigger5122, a peak detector 5124, a bottom detector 5126, a buffering device5128, and a processing circuit 5130. The edge trigger 5122 receives theTEZC signal Sref, and then triggers the peak detector 5124 and thebottom detector 5126 to determine one peak value and one peak value ateach edge of the TEZC signal Sref. Taking the peak detector 5124 forexample, it is triggered at a first edge of the TEZC signal Sref, andthen searches for a peak value until a second edge following the firstedge occurs. Therefore, when the peak detector 5124 is triggered due tothe second edge of the TEZC signal Sref, it will output a peak valuefound during a time interval between the first edge and the second edge.The bottom detector 5126 is defined to have similar operations to outputa bottom value found during a time interval between every two adjacentedges of the TEZC signal Sref. As known to those skilled in this art,each period of the TEZC signal Sref is representative of one track pitchin a radial direction of an optical disc. Therefore, during the trackjumping operation, the occurrence of each edge of the TEZC signal Srefindicates that the optical pick-up unit has passed a half track pitch.That is, the peak detector 5124 and the bottom detector 5126 aretriggered to output a peak value and a bottom value for every half trackpitch due to rising and falling edges of the TEZC signal Sref. Thebuffering device 5128 can be implemented using any volatile ornon-volatile storage components.

In a case where the detecting circuit 5104 is configured to detect atarget peak value and a target bottom value of the RFRP signal Sinwithin one period of the TEZC signal Sref (i.e., the moving window formonitoring the magnitude of the RFRP signal Sin is defined to be oneperiod of the TEZC signal Sref), two buffers are implemented in thebuffering device 5128 for storing a previous peak value PRE_MAX and aprevious bottom value PRE_MIN obtained according to a previous edge ofthe TEZC signal Sref, and two buffers are implemented in the bufferingdevice 5128 for storing a current peak value CUR_MAX and a currentbottom value CUR_MIN obtained according to a current edge following theprevious edge. The processing circuit 5130 is coupled to the bufferingdevice 5128 for determining the target peak value VMAX according to thecurrent peak value CUR_MAX and the previous peak value PRE_MAX and fordetermining the target bottom value VMIN according to the current bottomvalue CUR_MIN and the previous bottom value PRE_MIN. As shown in FIG.34, the processing circuit 5130 comprises a maximum value determiningunit 5132 and a minimum value determining unit 5134, where the maximumvalue determining unit 5132 is configured to select a maximum value outof the current peak value CUR_MAX and the previous peak value PRE_MAX toserve as the target peak value VMAX, and the minimum value determiningunit 5134 is configured to select a minimum value out of the currentbottom value CUR_MIN and the previous bottom value PRE_MIN to serve asthe target peak value VMIN. The computations are illustrated usingfollowing equations.VMAX=max (CUR_MAX, PRE_MAX)  (1)VMIN=min (CUR_MIN, PRE_MIN)  (2)

However, in another case where the detecting circuit 5104 is configuredto detect a target peak value and a target bottom value of the RFRPsignal Sin within N (N is greater that 1, for example, an integergreater than 1) periods of the TEZC signal Sref (i.e., the moving windowfor monitoring the magnitude of the RFRP signal Sin is defined to be Nperiods of the TEZC signal Sref), (2N−2) buffers are implemented in thebuffering device 5128 for storing (N−1) previous peak valuesPRE_MAX1−PRE_MAXn−1 and (N−1) previous bottom values PRE_MIN1−PRE_MINn−1obtained according to (N−1) previous successive edges of the TEZC signalSref, and two buffers are implemented in the buffering device 5128 forstoring a current peak value CUR_MAX and a current bottom value CUR_MINobtained according to a current edge immediately following the previoussuccessive edges. The maximum value determining unit 5132 is configuredto select a maximum value out of the current peak value CUR_MAX and the(N−1) previous peak values PRE_MAX1−PRE_MAXn−1 to serve as the targetpeak value VMAX, and the minimum value determining unit 5134 isconfigured to select a minimum value out of the current bottom valueCUR_MIN and the (N−1) previous bottom values PRE_MIN1−PRE_MINn−1 toserve as the target peak value VMIN. The computations are illustratedusing following equations.VMAX=max (PRE_MAX1, PRE_MAX2, . . . , PRE_MAXn−1, CUR_MAX)  (3)VMIN=max (PRE_MIN1, PRE_MIN2, . . . , PRE_MINn−1, CUR_MIN)  (4)

It should be noted that above cases are for illustrative purposes only,and are not meant to be limitations of the present invention.

Next, the decision logic 5106 is operative to determine a referencelevel (e.g., a slicer level of the RFRP signal) Lref according to thereceived target peak value VMAX and the target bottom value VMIN. Inthis embodiment, the decision logic 5106 determines the slicer levelLref by averaging the target peak value VMAX and the target bottom valueVMIN.Lref=(VMAX+VMIN)/2  (5)

It should be noted that the current slicer level Lref will be updated atthe time when the new target peak value VMAX and the target bottom valueVMIN are outputted from the processing circuit 130 at a next edge of theTEZC signal Sref since the moving window of monitoring the magnitude ofthe RFRP signal Sin is shifted forward continuously. After the slicerlevel Lref is generated, the comparator 5114 serves as a slicer forslicing the RFRP signal Sin through comparing the slicer level Lref andthe RFRP signal Sin, and then outputs the sliced signal Sout as thedesired mirror signal.

Additionally, the update controller 5108 is implemented to bypass theslicer level Lref determined by the decision logic 5106 to thecomparator 5114 or directly set the slicer level Lref outputted to thecomparator 5144 by an initial value Lini provided by the initial valuecontroller 5112. Some examples of setting the initial value Lini aregiven as below.

In a first example, the initial value controller 5112 directly set theinitial value Lini to the update controller 108 according to thefollowing equation:Lini=IN−(MAX−MIN)/2  (6)

In above equation (6), IN represents the RFRP signal Sin in thebeginning of the current track jumping operational period, MAXrepresents a specific maximum value outputted from the maximum valuedetermining unit 5132 in the previous track jumping operational period,and MIN represents a specific minimum value outputted from the minimumvalue determining unit 5134 in the previous track jumping operationalperiod. Preferably, the specific maximum value is the last target peakvalue VMAX found in the previous track jumping operational period, andthe specific minimum value is the last target bottom value VMIN found inthe previous operational period. In this example, the slicer level Lrefinitially set by the initial value Lini will be updated when a previouspeak value, a previous bottom value, a current peak value, and a currentbottom value are buffered in the buffering device 5128 if the slicerlevel setting scheme mentioned in above first case is implemented. Inaddition, the slicer level Lref initially set by the initial value Liniwill be updated when (N−1) previous peak values, (N−1) previous bottomvalues, a current peak value, and a current bottom value are buffered inthe buffering device 5128 if the slicer level setting scheme mentionedin above second case is implemented.

In a second example, the initial value controller 5112 is coupled to thebuffering device 5128 for controlling the initial value of the slicerlevel Lref by directly setting an initial current peak value, an initialprevious peak value, an initial current bottom value, and an initialprevious bottom value buffered in the buffering device 5128 according toa first predetermined value, a second predetermined value, a specificmaximum value (e.g., the above-mentioned MAX), a corresponding specificminimum value (e.g., the above-mentioned MIN) of the previous trackjumping operational period, and the RFRP signal Sin in the beginning ofthe current track jumping operational period (e.g., the above-mentionedIN). In this example, the initial value controller 5112 setsIN−(MAX−MIN) to the initial current bottom value, IN to the initialcurrent peak value, the first predetermined value to the initialprevious peak value, and the second predetermined value to the initialprevious bottom value. Preferably, the specific maximum value MAX is thelast target peak value VMAX found in the previous track jumpingoperational period, and the specific minimum value MIN is the lasttarget bottom value VMIN found in the previous track jumping operationalperiod. Additionally, the first predetermined value could be set by anyvalue less than or equal to a minimum of all possible bottom values ofthe RFRP signal Sin or set by the last minimum value found in theprevious track jumping operational period (i.e., MIN), and the secondpredetermined value could be set by any value greater than or equal to amaximum of all possible peak values of the RFRP signal Sin or set by thelast maximum value found in the previous track jumping operationalperiod (i.e., MAX).

In a third example, the buffering device 5128 for controlling theinitial value of the slicer level Lref by directly setting an initialcurrent peak value, an initial current bottom value, (N−1) initialprevious peak values, and (N−1) initial previous bottom values bufferedin the buffering device 5128 according to first predetermined values,second predetermined values, a specific maximum value (e.g., theabove-mentioned MAX), a corresponding specific minimum value (e.g., theabove-mentioned MIN) of the previous track jumping operational period,and the RFRP signal Sin in the beginning of the current track jumpingoperational period (e.g., the above-mentioned IN). In this example, theinitial value controller 5112 sets IN−(MAX−MIN) to the initial currentbottom value, IN to the initial current peak value, the firstpredetermined values to the (N−1) initial previous peak valuesrespectively, and the second predetermined values to the (N−1) initialprevious bottom values respectively. Preferably, the specific maximumvalue MAX is the last target peak value VMAX found in the previous trackjumping operational period, and the specific minimum value MIN is thelast target bottom value VMIN found in the previous track jumpingoperational period. Additionally, the first predetermined values eachcould be set by any value less than or equal to a minimum of allpossible bottom values of the RFRP signal Sin or set by the last minimumvalue found in the previous track jumping operational period (i.e.,MIN), and the second predetermined values each could be set by any valuegreater than or equal to a maximum of all possible peak values of theRFRP signal Sin or set by the last maximum value found in the previoustrack jumping operational period (i.e., MAX).

If the initial value controller 5112 is only designed to support theinitial value setting scheme disclosed in above first example, thecircuit complexity of the initial controller 5112 is high due toadditional computation is needed for determining the initial value Liniaccording to the aforementioned equation (6). However, if the initialvalue controller 5112 is only designed to support the initial valuesetting scheme disclosed in above second example or third example, thecircuit complexity of the initial controller 5112 is reduced since noextra computation is needed. As a result, the production cost is reducedaccordingly.

Please refer to FIG. 35 in conjunction with FIG. 34. FIG. 35 is a timingdiagram illustrating the generation of the reference level Lref and thesliced signal Sout shown in FIG. 34 according to an embodiment of thepresent invention. As mentioned above, in one exemplary embodiment ofthe present invention, the input signal Sin is an RFRP signal, thereference signal Sref is a TEZC signal, the reference level Lref is aslicer level used for slicing the RFRP signal, and the sliced signalSout is a mirror signal. Suppose that the detecting circuit 5104 isconfigured to detect a target peak value VMAX and a target bottom valueVMIN of the RFRP signal Sin within one period of the TEZC signal Sref(i.e., the moving window for monitoring the magnitude of the RFRP signalSin is defined to be one period of the TEZC signal Sref). At time Tb2,the peak detector 5124 is triggered by a falling edge of the TEZC signalSref to determine and output a peak value V1 of the half track pitch P1;simultaneously, the bottom detector 5126 is triggered by the samefalling edge of the TEZC signal Sref to determine and output a bottomvalue V2 of the half track pitch P1. At time Tb3, the peak detector 5124is triggered by a rising edge of the TEZC signal Sref to determine andoutput a peak value V3 of the half track pitch P2 following the halftrack pitch P1; simultaneously, the bottom detector 5126 is triggered bythe same rising edge of the TEZC signal Sref to determine and output thebottom value V2 of the half track pitch P2 following the half trackpitch P1. At this moment, the buffering device 5128 has stored the peakvalue V1 as the previous peak value PRE_MAX, the bottom value V2 as theprevious bottom value PRE_MIN, the peak value V3 as the current peakvalue CUR_MAX, and the bottom value V2 as the current bottom valueCUR_MIN. Therefore, the maximum value determining unit 5132 outputs thepeak value V3 as the target peak value VMAX, and the minimum valuedetermining unit 5134 outputs the bottom value V2 as the target bottomvalue VMIN. Next, the decision logic 5106 updates the slicer level Lrefaccording to an average value of the target peak value VMAX and thetarget bottom value VMIN. As a result, the updated slicer level Lrefbecomes (V3+V2)/2 as shown in FIG. 35. Since a person skilled in the artcan readily understand the disclosed slicer level updating occurring atother edges of the TEZC signal Sref after reading above description,further description is not repeated here for the sake of brevity. Pleasenote that the movement of the optical pick-up unit relative to theoptical disc is inversed at time Tb4. However, the slicer level Lref iswell controlled to make the comparator 5114 output an accurate slicedsignal Sout. Compared to the related art, the performance of the trackjumping (track seeking) operation is improved.

As shown in FIG. 35, an on-track signal TRON is additionally presented.The on-track signal TRON serves as a system flag for indicating if thecurrent operation mode is an on-track mode or a track-jumping(track-seeking) mode. For example, when the on-track signal TRON ismaintained at a high logic level, it means that the optical pick-up unitis operated under the on-track mode; however, when the on-track signalTRON has a transition from a high logic level to a low logic level, itmeans that the optical pick-up unit enters the track-jumping mode, andwhen the on-track signal TRON has a transition from a low logic level toa high logic level, it means that the optical pick-up unit leaves thetrack-jumping mode. Referring to FIG. 35, the track-jumping mode isactivated during an operational period from Tb1 to Tb1′. At time T1, anew track jumping operation starts. Therefore, when the on-track signalTRON has a transition from a high logic level to a low logic level attime Tb1, the initial value controller 5112 is enabled to control theinitial value of the slicer level Lref. When a next track jumpingoperation is activated, the target peak value VMAX and the target bottomvalue VMIN obtained due to an edge of the TEZC signal Sref occurring attime T1′ are used for controlling the initial value of the slicer levelLref.

Moreover, when the optical pick-up unit is moving on a defect area ofthe optical disc, the waveform of the RFRP signal becomes abnormal.Therefore, the present invention provides a protection circuit 5110 toprevent the slicer level from being erroneously biased due to thedefects. As shown in FIG. 34, the protection circuit 5110 is coupled tothe update controller 5108 and operative to control the updatecontroller 5108 to hold the slicer level Lref when a defect detectionresult indicates that a defect on the optical disc is found. Since howto detect the defects is well known to those skilled in this art,further description is omitted for brevity. Please refer to FIG. 36.FIG. 36 is a diagram illustrating the protection scheme according to anembodiment of the present invention. A defect indication signal Sdi isprovided to indicate if a defect on the optical disc is found. At timeTb5, the defect indication signal Sdi has a transition from a low logiclevel to a high logic level, meaning that a defect on the optical discis identified. Therefore, the protection circuit 5110 instructs theupdate controller 5108 to hold the current slicer level Lref. At timeTb5′, the defect indication signal Sdi has a transition from a highlogic level to a low logic level, meaning that the optical pick-up unithas moved to a defect-free area of the optical disc. Therefore, theprotection circuit 110 allows the update controller 5108 to bypass thecalculated slicer level Lref to the following comparator 5114.

Please refer to FIG. 37. FIG. 37 is a flow chart of processing an RFRPsignal to generate a mirror signal according to an embodiment of thepresent invention. Suppose that the same result is substantiallyobtained. The steps are not limited to be executed according to theexact order shown in FIG. 37. The flow of generating the mirror signalincludes the following steps:

Step 400: Start.

Step 402: Is a track-jumping (track-seeking) mode enabled? If yes, go tostep 404; otherwise, repeat step 402 to keep monitoring.

Step 404: Set an initial value of a slicer level.

Step 406: Compare an RFRP signal with the slicer level to output/updatethe mirror signal.

Step 408: Is an on-track mode enabled? If yes, go to step 402;otherwise, go to step 410.

Step 410: Detect a target peak value and a target bottom value of theRFRP signal within an integer multiple of a period of a TEZC signal.

Step 412: Average the target peak value and the target bottom value togenerate an average value.

Step 414: Update the slicer level using an average value. Go to step406.

The method is performed by the apparatus 5100 shown in FIG. 34. Sincethe details associated with functions and operations of the componentsin the apparatus 5100 have been given above, further description of thesteps shown in FIG. 37 is omitted for the sake of brevity.

Please refer to FIG. 38. FIG. 38 is a diagram illustrating the structureof the digital signal processor 5300 of the signal processing apparatus200 according to an embodiment of the present invention. Generally, thesignal processing apparatus 200 is realized with a digital signalprocessor (DSP). As shown in FIG. 38, the signal generator 5300comprises a program unit 5301, a decoder 5302, an I/O unit 5303, aflip-flop module 5304, and a calculation unit 5305. The flip-flop module5304 comprises a plurality of flip-flops. The calculation unit 5305comprises a plurality of arithmetic logic units.

Please continue referring to FIG. 38. The program unit 5301 is disposedfor storing a program and transmitting instructions according to theprogram. The decoder 5302 is coupled to the program unit 5301 forreceiving the instructions from the program unit 5301 and accordinglytransmits control signals to the I/O unit 5303, the flip-flop module4304, and the calculation unit 5305. The I/O unit 5303 serves as aninterface for receiving the digital photo diode signals and outputtingthe digital servo signals and the digital detection signals. The digitaldetection signals can be RF zero-crossing signals (RFZC), trackingzero-crossing signals (TZC), or RAM-Header signals. The flip-flop module5304 is coupled between the I/O unit 5303 and the calculation unit 5305for storing signals from the I/O unit 5303 and from the calculation unit5305. The calculation unit 5305 uses the plurality of ALUs forcalculating the digital photo diode signals and the digital detectionsignals from the flip-flop module 5304 and storing the calculationresult (servo signals or detection signals) in the flip-flop module5304.

Please continue referring to FIG. 38. It is assumed that the samplingrate of the analog/digital device is 1 MHz, a low-pass filter designedin the calculation 5305 needs 5 instructions to operate and an adderdesigned in the calculation 5305 needs one instruction to operate, andto calculate a result as the digital servo signal needs 60 low-passfilters and 60 adders. Because the flip-flop module 5304 operatesmultiple instructions per program counter, that is, the flip-flop module5304 can provide data to different devices at the same time, thus thecalculation unit 5305 operates multiple instructions per programcounter. Based on the above assumption, to generate a digital servosignal needs only 6 program counters (1*5+1). Therefore, the frequencyof the signal generator 5300 only has to be 6 MHz, which can be designedeasily.

FIG. 39 is a block diagram of an exemplary automatic control systemaccording to the invention, comprising analog-to-digital converter (ADC)6220, down sampling circuit 6230, digital preprocessing unit 6222,comparator 6224, digital post processing unit 6226, anddigital-to-analog converter (DAC) 6228. Analog to digital converter(ADC) 6220 is coupled to down sampling circuit 6230, digitalpreprocessing unit 6222, comparator 6224, digital post processing unit6226, and then to digital-to-analog converter (DAC) 6228.

In an example, automatic power control system 6300 provides automaticpower control of a laser diode in an optical disc drive Analog inputsignal S_(in) is a laser beam reflection sensed by a photo detector inan OPU of the system, and corresponds to power level of the laser diode.ADC 6220 converts analog input signal S_(in) to digital sampled dataD_(s), down converted by down sampling rate R to generate down sampleddata D_(d) in down sampling circuit 6230, where the down sampling rateis a ratio less than a unity. Digital preprocessing unit 6222preprocesses down sampled data D_(s) to, for example, filter noise andsmooth the signal, and outputs preprocessed data D_(pre) to comparator6224. Comparator 6224 compares preprocessed data D_(pre) and targetvalue D_(target) to generate error data D_(e), filtered in digitalpost-processing unit 6226 to generate smooth output D_(post), convertedto analog control signal S_(c) in digital-to-analog converter 6228.Analog control signal S_(c) in turn controls a driving current to thelaser diode such that the power level thereof remains stable withouterror data D_(e).

FIG. 40 is a block diagram of an exemplary down sampling circuitaccording to the invention, incorporated in the automatic power controlsystem in FIG. 39, comprising down sampler 6240, counter 6242, andcontroller 6244. Controller 6244 is coupled to counter 6242, andsubsequently to down sampler 6240.

Down sampler 6240 receives a predetermined amount of sampled data D_(s)from ADC 6220 to generate down sampled (representation) data D_(d) whensampled data Ds is valid. Down sampler 6240 may be an accumulatoraccumulating the predetermined amount of sampled data D_(s) to generateaccumulated down sampled data D_(d), each sampled data D_(s) is assignedto an equal or different weight (coefficient) in the accumulation. Downsampler 6240 may be a finite impulse response (FIR) filter. The validityof sampled data D_(s) may be indicated by valid data indication D_(rdy)that provides a pulse for each valid data.

Counter 6242 receives valid data indication D_(rdy) to establish anamount of valid sampled data, and resets the down sampler 6240 when theamount of valid sampled data equals or exceeds the predetermined amount.

Controller 6244 receives valid signal S_(valid) indicating the validityof sampled data Ds, enables counter 6242 when sampled data D_(s) isvalid, and disables counter 6242 when invalid. Controller 6244 maydisable counter 6242 by resetting or holding the counter 6242.Controller 6244 may reset counter 6242 by reset signal S_(reset) andhold counter 6242 by hold signal S_(hold).

Down sampling circuit 6230 may operate in four modes as depicted in FIG.41, a timing diagram of selected signals according to the invention,incorporated in the down sampling circuit in FIG. 40, comprising validsignal S_(valid), valid sampled count N_(valid), and down sampled dataD_(d). Valid signal S_(valid) is logic “high” for invalid data, andlogic “low” for valid data. For automatic power control and servocontrol, valid signal S_(valid) is high during writing data, and lowduring read. In the case of automatic power control, the read data aredown sampled to provide a representation of reflected laser light powerduring read, and the laser power is adjusted so that the representationcan meet the requirement set by target data D_(target).

In the first mode, controller 6244 does not disable counter 6242regardless of valid signal S_(valid) and counter 6242 runs continuouslysuch that down sampler 6240 generates a down sampled data D_(d) everypredetermined amount of sampled data D_(s). Down sampler 6240 mayreceive valid or invalid sample data D_(s) to generate down sampled dataD_(d). Down sampler 6240, however, discards the down sampled data D_(d)when any of the sampled data Ds is invalid, such that the down sampleddata D_(d) is only output when all of the predetermined amount ofsampled data is valid. The first down sampled data D_(d) in the validperiod (period 6506) is discarded to ensure validity, at the expense ofcircuit efficiency.

In the second mode, controller 6244 resets counter 6242 wheneverreceiving invalid data signal S_(valid). Upon reset, Counter 6242 inturn resets down sampler 6240, so that down sampler 6240 discards allsampled data D_(s) therein and restarts the down sampling operationagain after sampled data Ds is valid (S_(valid) is logic “low”). Thesecond mode is more efficient than the first since the first downsampled data D_(d) in the valid period (period 6506) is not wasted,while the last down sampled data D_(d) immediately before the invalidperiod (period 6504) is dumped.

In the third mode, controller 6244 holds counter 6242 upon receivinginvalid signal S_(valid). Counter 6242 stops calculating the amount ofvalid sampled data and suspends down sampler 6240. Down sampler 6240 isdisabled and discards any incoming sampled data Ds. Upon receiving validsignal S_(valid), counter 6244 enables counter 6242, in turn to enabledown sampler 6240 to complete the down sampling operation. The thirdmode is more efficient than the first and the second ones, since everysampled data Ds in valid period is not wasted.

In the fourth mode, controller 6244 does not disable counter 6244 uponinvalid signal S_(valid). Counter 6242 runs continuously and downsampler 6240 generates a down sampled data D_(d) every predeterminedamount of sampled data D_(s). Upon detection of invalid data, downsampler 6240 recycles the valid data immediately before the invalid datafor the accumulation, thereby generating a down sampled data D_(d) everypredetermined count. The third mode is more efficient than the first andthe second ones, since every sampled data D_(s) in valid period is notwasted.

FIG. 42 is a flowchart of an exemplary automatic control circuit method,incorporated in the automatic control circuit in FIG. 39.

In Step S6600, automatic power control 6300 is initialized and analoginput signal S_(in) is detected in Step S6602.

In Step S6604, ADC 6220 converts analog input signal S_(in) to digitalfor sampled data D_(s), and down sampling circuit 6230 performs downsampling operation thereon to generate down sampled data Ds in StepS6606.

In Step S6608, digital preprocessing unit 6222 obtains down sampled dataD_(s) to perform filtering thereon, removing noise from and smoothingdown sampled data D_(s) to generate preprocessed data D_(pre).

In step S6610, comparator 6224 compares preprocessed data D_(pre) withtarget data D_(target) to generate error data D_(e) indicating adifference therebetween. Next post-processing unit 6226 filters andsmoothes error data D_(e) to provide post processed data D_(post) instep S6612.

In Step S6614, digital to analog converter 6228 converts post processeddata D_(post) to analog control signal Dc, thereby controlling thedriving current to the optical diode and the power level of the laserbeam for a reading operation.

FIG. 43 is a flowchart of an exemplary down sampling method,incorporated in the method in FIG. 42 and the down sampling circuit inFIG. 40.

Upon initialization of down sampling circuit 6230, controller 6244determines whether sampled data D_(s) is valid in Step S6700, continuesstep S6702 if sampled data D_(s) is valid, and step S6708 otherwise. Thevalidity of sampled data D_(s) is indicated by valid data signalS_(valid), with logic “low” being valid and “high” being invalid.

Next counter 6242 calculates the amount of sampled data D_(s) in stepS6702, and down sampler receives sampled data D_(s) to generate downsampled data D_(d) in step S6704. Down sampler 6240 may accumulate eachsampled data D_(s) to generate an accumulation for down sampled dataD_(d).

Next in step S6706, when the amount of sampled data D_(s) equals orexceeds the predetermined count, down sampler 6240 and counter 6242 arereset to reinitialize another down sampling operation in step S6700.

In Step S6708, controller determines whether down sampling circuit 6230is in the high speed mode if sampled data D_(s) is invalid, proceedsstep S6710 if so, and step S6712 otherwise.

In Step S6710, down sampling circuit 6230, if in high speed mode, holdsboth counter 42 and down sampler 6240, and continues checking thevalidity of subsequent sampled data D_(s) in step S6700. Counter 6242stops calculating the amount of sampled data D_(s) and down sampler 6240holds the generation of down sampled data D_(d).

In Step S6712, down sampling circuit 6230, if not in high speed mode,resets both counter 6242 and down sampler 6240, so that the downsampling process is reinitialized in step S6700.

While the invention has been described by way of example and in terms ofpreferred embodiment, it is to be understood that the invention is notlimited thereto. To the contrary, it is intended to cover variousmodifications and similar arrangements (as would be apparent to thoseskilled in the art). Therefore, the scope of the appended claims shouldbe accorded the broadest interpretation to encompass all suchmodifications and similar arrangements.

1. An apparatus for controlling servo signal gains of an optical discdrive, wherein the apparatus adjusts the gains of a plurality of servosignals controlling a servo system of the optical disc drive accordingto a closed-loop mode or a state-reloading mode whenever the opticaldisk drive encounters an operating state transition, comprising: inclosed-loop mode, at least one AGC loop, compensating the gains of theservo signals with a selectable bandwidth during a specific period afterthe operating state transition to accelerate the convergence of theservo signals; and in state-reloading mode, at least one AGC loop,reloading the previously saved convergence values or pre-determinedvalues as the initial values according to the current operating stateimmediately after the operating state transition to accelerate theconvergence of the servo signals.
 2. The apparatus as claimed in claim1, wherein the operating state transition occurs whenever the operatingstate of the optical disc drive is changed, and the operating statecomprises a write state in which data is being written to the opticaldisc, a blank state in which a blank zone of the optical disc is beingread, and a data state in which a data zone of the optical disc is beingread.
 3. The apparatus as claimed in claim 2, wherein the apparatus cansave the convergence loop-ratio values of the at least one AGC loop, andthen reload the saved convergence loop-ratio values of the at least oneAGC loop corresponding to the corresponding operating state as theinitial loop-ratio values of the at least one AGC loop after theoperating state transition to determine the gains of the servo signalsin state-reloading mode.
 4. The apparatus as claimed in claim 1, whereinthe servo signals include a tracking error signal controlling a trackingoperation of the optical disc drive, a focusing error signal controllinga focusing operation of the optical disc drive, and a main-beam additionsignal or a sub-beam addition signal indicating the summation of theintensity of the main-beam or sub-beam.
 5. The apparatus as claimed inclaim 2, wherein the apparatus determines an operating state transitionaccording to a write signal and a blank signal, wherein the write signalindicates a switch between a writing operation and a reading operationof the optical disc drive, and the blank signal indicates a switchbetween a blank zone and a data zone read by the optical disc drive. 6.The apparatus as claimed in claim 1, wherein the servo signals aredigital signals, and the gains of the servo signals are adjusted by theapparatus in a digital domain.
 7. An apparatus for controlling servosignal gains of an optical disc drive, comprising: a first automaticgain control module, adjusting a loop ratio of a main-beam to controlthe gains of a plurality of servo signals whenever the optical diskdrive encounters an operating state transition in which the reflectivityof a read portion of an optical disc or the intensity of the main-beamincident to the optical disc is changed, wherein the servo signalscontrol a servo system of the optical disc drive; and a second automaticgain control module, adjusting the gains of the sub-beam servo signalsaccording to a main-beam sub-beam ratio whenever the optical disk driveencounters the operating state transition, wherein the main-beamsub-beam ratio is calculated according to both the reflectionintensities of the main-beam and a sub-beam reflected from an opticaldisc.
 8. The apparatus as claimed in claim 7, wherein the servo signalsinclude a tracking error signal controlling a tracking operation of theoptical disc drive, a focusing error signal controlling a focusingoperation of the optical disc drive, and a main-beam addition signal ora sub-beam addition signal indicating the summation of the intensity ofthe main-beam or a sub-beam.
 9. The apparatus as claimed in claim 8,wherein the first automatic gain control module comprises: a loop ratiogeneration module, calculating the loop ratio according to a desiredtarget intensity and the reflection intensity of the current main-beam;and a first gain control logic, coupled to the loop ratio generationmodule, determining the gains of the servo signals according to the loopratio.
 10. The apparatus as claimed in claim 8, wherein the secondautomatic gain control module comprises: a main-beam sub-beam ratiogeneration module, calculating the main-beam sub-beam ratio according tothe reflection intensity of the current main-beam and the reflectionintensity of the current sub-beam; and a second gain control logic,coupled to the main-beam sub-beam ratio generation module, determiningthe gains of sub-beam servo signals for synthesizing the servo signalsaccording to the main-beam sub-beam ratio.
 11. The apparatus as claimedin claim 9, wherein the first gain control logic comprises: a firstmultiplier, multiplying a first tracking error gain by the loop ratio toobtain a second tracking error gain; a second multiplier, multiplying afirst focusing error gain by the loop ratio to obtain a second focusingerror gain; a third multiplier, multiplying a first main-beam additiongain or a sub-beam addition gain by the loop ratio to obtain a secondMain-beam addition gain or a sub-beam addition gain; and a first controlmodule, selecting the first or the second tracking error gain as thegain of the tracking error signal, selecting the first or the secondfocusing error gain as the gain of the focusing error signal, selectingthe first or the second main-beam addition gain or a sub-beam additiongain as the gain of the main-beam addition gain or a sub-beam additionsignal.
 12. The apparatus as claimed in claim 10, wherein the secondgain control logic comprises: a fourth multiplier, multiplying a firstsub-beam summation gain by the main-beam sub-beam ratio to obtain asecond sub-beam summation gain; a fifth multiplier, multiplying a firstsub-beam push-pull gain by the main-beam sub-beam ratio to obtain asecond sub-beam push-pull gain; a sixth multiplier, multiplying a firstsub-beam focusing error gain by the main-beam sub-beam ratio to obtain asecond sub-beam focusing error gain; and a second control module,selecting the first or the second sub-beam summation gain as the gain ofa sub-beam summation signal, selecting the first or the second sub-beampush-pull gain as the gain of a sub-beam push-pull signal, selecting thefirst or the second sub-beam focusing error gain as the gain of asub-beam focusing error signal; wherein the sub-beam summation signal,the sub-beam push-pull signal, and the sub-beam focusing error signalare generated from the reflection signals of the sub-beam byrespectively synthesizing the sub-beam addition signal, the trackingerror signal, and the focusing error signal.
 13. The apparatus asclaimed in claim 7, wherein the operating state transition occurswhenever an operating state of the optical disc drive is changed, andthe operating state comprises a write state in which data is written tothe optical disc, a blank state in which blank zone of the optical discis read, and a data state in which data zone of the optical disc isread.
 14. The apparatus as claimed in claim 7, wherein the servo signalsare digital signals, and the gains of the servo signals are adjusted bythe apparatus in a digital domain.
 15. The apparatus as claimed in claim8, wherein the first automatic gain control module controls theamplification process of a tracking error signal generation module whichgenerates the tracking error signal according to a main-beam push-pullsignal and a sub-beam push-pull signal, a focusing error signalgeneration module which generates the focusing error signal according toa main-beam focusing error signal and a sub-beam focusing error signal,and a sub-beam addition signal generation module which generates thesub-beam addition signal according to a main-beam summation signal and asub-beam summation signal; wherein the main-beam push-pull signal, themain-beam focusing error signal, and the main-beam summation signal aregenerated from the reflection signals of the main-beam, and the sub-beampush-pull signal, the sub-beam focusing error signal, and the sub-beamsummation signal are generated from the reflection signals of thesub-beam.
 16. The apparatus as claimed in claim 15, wherein the secondautomatic gain control module controls the amplification process of asub-beam summation module which generates the sub-beam summation signal,a sub-beam push-pull module which generates the sub-beam push-pullsignal, and a sub-beam focusing error module which generates thesub-beam focusing error signal.
 17. A method for controlling servosignal gains of an optical disc drive, wherein a plurality of servosignals controls a servo system of the optical disc drive, the methodcomprising: adjusting the servo signals gains according to a closed-loopmode or a state-reloading mode whenever the optical disk driveencounters an operating state transition; in the closed-loop mode,compensating the gains of the servo signals with a selectable bandwidthof at least one AGC loop during a specific period after the operatingstate transition to accelerate the convergence of the servo signals; andin the state-reloading mode, immediately reloading previously savedconvergence values of the corresponding operating state orpre-determined values as the initial values of at least one AGC loopafter the operating state transition to accelerate the convergence ofthe servo signals.
 18. The method as claimed in claim 17, wherein theoperating state transition occurs whenever an operating state of theoptical disc drive is changed, and the operating state comprises a writestate in which data is being written to the optical disc, a blank statein which blank zone of the optical disc is being read, and a data statein which data zone of the optical disc is being read.
 19. The method asclaimed in claim 18, wherein the reloading of the previously savedconvergence values further comprises: respectively saving convergencevalues of AGC loop ratios determining the gains of the servo signals inadvance according to the operating states of the optical disc driveafter the operating state transition; and assigning the savedconvergence values of the AGC loop ratios corresponding to the operatingstates as the initial values of the AGC loop ratios to determine thegains of the servo signals after the operating state transition instate-reloading mode.
 20. The method as claimed in claim 18, wherein themethod further comprises determining an occurrence of the operatingstate transition according to a write signal and a blank signal, whereinthe write signal indicates a switch between a writing operation and areading operation of the optical disc drive, and the blank signalindicates a switch between the blank zone and the data zone read by theoptical disc drive.
 21. The method as claimed in claim 17, wherein theservo signals include a tracking error signal controlling a trackingoperation of the optical disc drive, a focusing error signal controllinga focusing operation of the optical disc drive, and a main-beam additionsignal or a sub-beam addition signal indicating the summation of theintensity of the main-beam or sub-beam.
 22. The method as claimed inclaim 17, wherein the servo signals are digital signals, and the gainsof the servo signals are adjusted in a digital domain.